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Statistics Quiz

Statistics Quiz: Describing Events In Sample Spaces

Practice Describing Events In Sample Spaces in Statistics with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

Question 1 / 20

0 of 20 answered

According to the sample space S={1,2,3,4,5,6,7,8}S=\{1,2,3,4,5,6,7,8\}S={1,2,3,4,5,6,7,8} for selecting one card labeled 1–8 from a bag, event AAA is the set of even outcomes and event BBB is the set of outcomes greater than 5. Which expression represents A∩BA\cap BA∩B (A and B)?

Select an answer to continue

What this quiz covers

This quiz focuses on Describing Events In Sample Spaces, giving you a quick way to practice the rules, question types, and explanations that matter most for Statistics.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

All questions

Question 1

According to the sample space S={1,2,3,4,5,6,7,8}S=\{1,2,3,4,5,6,7,8\}S={1,2,3,4,5,6,7,8} for selecting one card labeled 1–8 from a bag, event AAA is the set of even outcomes and event BBB is the set of outcomes greater than 5. Which expression represents A∩BA\cap BA∩B (A and B)?

  1. {7}\{7\}{7}
  2. {1,2,3,4,5,6,7,8}\{1,2,3,4,5,6,7,8\}{1,2,3,4,5,6,7,8}
  3. {6,8}\{6,8\}{6,8} (correct answer)
  4. {2,4,6,8}\{2,4,6,8\}{2,4,6,8}

Explanation: This question involves identifying the intersection of two events in a sample space. An event is a subset of the sample space, which here is S = {1,2,3,4,5,6,7,8}, representing possible outcomes when selecting a card. The intersection A ∩ B means the outcomes that satisfy both event A (even numbers) and event B (numbers greater than 5), or in plain language, 'A and B.' The correct set {6,8} matches this because 6 is even and greater than 5, and 8 is even and greater than 5, both from S. A tempting distractor like {2,4,6,8} fails because it represents only A, confusing intersection with the union of events. To approach these problems, translate the words 'and' to intersection, then list outcomes from S that satisfy both conditions exactly. Always ensure the outcomes match the listed elements in S precisely, without adding or assuming extras.

Question 2

According to the sample space S={apple,banana,carrot,dates}S=\{\text{apple},\text{banana},\text{carrot},\text{dates}\}S={apple,banana,carrot,dates} for randomly selecting one item, event AAA is “the item is a fruit” and event BBB is “the item starts with the letter b.” Which set represents A∩BA\cap BA∩B (A and B)?

  1. {banana}\{\text{banana}\}{banana} (correct answer)
  2. {banana,carrot}\{\text{banana},\text{carrot}\}{banana,carrot}
  3. {carrot}\{\text{carrot}\}{carrot}
  4. {apple,banana,dates}\{\text{apple},\text{banana},\text{dates}\}{apple,banana,dates}

Explanation: This question entails finding the intersection of events in an item selection sample space. An event is a subset of the sample space S = {apple,banana,carrot,dates}, listing possible items. A ∩ B represents outcomes both in A (fruit) and B (starts with b), or 'A and B' in basic terms. The correct set {banana} is right because banana is a fruit starting with b, precisely as in S. A distractor such as {apple,banana,dates} shows only A, mistaking intersection for union. Convert 'and' to intersection, find outcomes meeting both criteria from S, and list them verbatim. This ensures the event aligns exactly with S's specified outcomes.

Question 3

Using the outcomes listed, S={cat,dog,fish,bird}S=\{\text{cat},\text{dog},\text{fish},\text{bird}\}S={cat,dog,fish,bird} for randomly selecting one sticker, let event AAA be “selects a pet that lives in water” and let event BBB be “selects a pet that can fly.” Which set represents A∪BA\cup BA∪B (A or B)?

  1. {fish}\{\text{fish}\}{fish}
  2. {fish,bird}\{\text{fish},\text{bird}\}{fish,bird} (correct answer)
  3. {cat,dog}\{\text{cat},\text{dog}\}{cat,dog}
  4. {cat,dog,fish,bird}\{\text{cat},\text{dog},\text{fish},\text{bird}\}{cat,dog,fish,bird}

Explanation: This question involves finding the union of two events in a sample space of pet stickers. An event is a subset of the sample space S = {cat,dog,fish,bird}, listing all selectable outcomes. The union A ∪ B means outcomes in A (lives in water) or B (can fly), or simply 'A or B' in everyday terms. The correct set {fish,bird} works because fish is in A and bird is in B, both exactly as listed in S without overlap. A distractor such as {cat,dog,fish,bird} fails by including all of S, mistaking union for the entire space rather than specific events. A useful strategy is to convert 'or' to union, merge the outcomes of each event from S, and exclude duplicates. Emphasize matching S's exact outcomes to accurately represent the events described.

Question 4

According to S={1,2,3,4,5,6}S=\{1,2,3,4,5,6\}S={1,2,3,4,5,6} for rolling one standard number cube, event A={x∈S∣x is odd}A=\{x\in S\mid x\text{ is odd}\}A={x∈S∣x is odd} and event B={x∈S∣x≥4}B=\{x\in S\mid x\ge 4\}B={x∈S∣x≥4}. Which set of outcomes represents event BBB?

  1. {4,5,6}\{4,5,6\}{4,5,6} (correct answer)
  2. {1,3,5}\{1,3,5\}{1,3,5}
  3. {3,4,5,6}\{3,4,5,6\}{3,4,5,6}
  4. {1,2,3}\{1,2,3\}{1,2,3}

Explanation: This question tests identifying a single event as a subset in the context of a die roll. An event is a subset of the sample space S = {1,2,3,4,5,6}, which enumerates all possible outcomes. Here, event B is defined as outcomes where x ≥ 4, meaning numbers 4 or higher in plain language. The correct set {4,5,6} aligns because 4, 5, and 6 are all ≥ 4 and directly from S, such as 5 satisfying the condition. A distractor like {1,3,5} might tempt by showing odds, confusing B with event A (odds) instead of focusing on B's definition. To solve these, translate the event description to its set operation (here, a basic subset), then list matching outcomes from S precisely. Always verify against S's exact listings to ensure no mismatches in representation.

Question 5

Based on the sample space shown, S={(H,H),(H,T),(T,H),(T,T)}S=\{(H,H),(H,T),(T,H),(T,T)\}S={(H,H),(H,T),(T,H),(T,T)} for flipping two coins (first flip, second flip), let event AAA be “exactly one head” and event BBB be “the first flip is a head.” Which expression represents A∪BA\cup BA∪B (A or B)?

  1. {(H,T)}\{(H,T)\}{(H,T)}
  2. {(H,H),(H,T),(T,H)}\{(H,H),(H,T),(T,H)\}{(H,H),(H,T),(T,H)} (correct answer)
  3. {(H,H),(H,T),(T,H),(T,T)}\{(H,H),(H,T),(T,H),(T,T)\}{(H,H),(H,T),(T,H),(T,T)}
  4. {(H,T),(T,H)}\{(H,T),(T,H)\}{(H,T),(T,H)}

Explanation: This question asks for the union of two events based on a sample space for coin flips. An event is a subset of the sample space S = {(H,H),(H,T),(T,H),(T,T)}, detailing all possible paired outcomes. The union A ∪ B represents outcomes that are in A (exactly one head) or B (first flip head), or in plain language, 'A or B.' The correct set {(H,H),(H,T),(T,H)} fits because (H,H) is in B, (H,T) is in both, and (T,H) is in A, all drawn from S. A common distractor like {(H,T),(T,H)} errs by showing only A, confusing union with intersection. For similar questions, translate 'or' to union, combine outcomes from both events without duplicates, using only those listed in S. This ensures the event matches S exactly, focusing on inclusive 'or' for complete coverage.

Question 6

According to the sample space S={M,T,W,Th,F}S=\{\text{M},\text{T},\text{W},\text{Th},\text{F}\}S={M,T,W,Th,F} for randomly selecting one weekday (Monday through Friday), event AAA is “the day starts with the letter T.” Which set of outcomes represents event AAA?

  1. {T,Th}\{\text{T},\text{Th}\}{T,Th} (correct answer)
  2. {Th}\{\text{Th}\}{Th}
  3. {M,W,F}\{\text{M},\text{W},\text{F}\}{M,W,F}
  4. {M,T,W,Th,F}\{\text{M},\text{T},\text{W},\text{Th},\text{F}\}{M,T,W,Th,F}

Explanation: This question is about identifying a single event as a subset in a weekday selection scenario. An event is a subset of the sample space S = {M,T,W,Th,F}, representing abbreviated weekdays. Event A is defined as days starting with T, meaning those specific initials in plain terms. The correct set {T,Th} corresponds because T (Tuesday) and Th (Thursday) both start with T and are listed in S. A distractor like {Th} might fail by excluding T, misunderstanding the full scope of 'starts with T.' To handle this, translate the event phrase to a subset operation, then enumerate matching outcomes straight from S. Insist on exact matches to S's outcomes for precise event representation.

Question 7

Using the outcomes listed in the sample space S={R1,R2,R3,B1,B2,B3}S=\{R1,R2,R3,B1,B2,B3\}S={R1,R2,R3,B1,B2,B3} for spinning a spinner that can land on Red 1, Red 2, Red 3, Blue 1, Blue 2, or Blue 3: Event AAA is “lands on a Red outcome.” Which set represents AcA^cAc (not A)?

  1. {B1,B2,B3}\{B1,B2,B3\}{B1,B2,B3} (correct answer)
  2. {R1,R2,R3,B1,B2,B3}\{R1,R2,R3,B1,B2,B3\}{R1,R2,R3,B1,B2,B3}
  3. {R1,R2,R3}\{R1,R2,R3\}{R1,R2,R3}
  4. {R1,B1}\{R1,B1\}{R1,B1}

Explanation: This question focuses on the complement of an event within a given sample space. An event is a subset of the sample space S = {R1,R2,R3,B1,B2,B3}, which lists all possible spinner outcomes. The complement A^c means all outcomes in S that do not belong to A (landing on Red), or in plain language, 'not A.' The correct set {B1,B2,B3} matches because these are the Blue outcomes, like B1, which is not Red and is explicitly listed in S. A tempting distractor such as {R1,R2,R3,B1,B2,B3} fails by representing the entire S, mistaking complement for the union with A. A transferable strategy is to translate 'not' to complement, subtract the event's outcomes from S, and list only the remaining ones exactly as in S. Remember, event descriptions must align perfectly with S's listed outcomes to avoid errors.

Question 8

Based on the sample space S={A,B,C,D,E}S=\{\text{A},\text{B},\text{C},\text{D},\text{E}\}S={A,B,C,D,E} for randomly choosing one letter tile, event AAA is “the letter is a vowel” and event BBB is “the letter comes after C in the alphabet (within S).” Which set represents A∩BA\cap BA∩B (A and B)?

  1. {A,B,C,D,E}\{\text{A},\text{B},\text{C},\text{D},\text{E}\}{A,B,C,D,E}
  2. {A,E}\{\text{A},\text{E}\}{A,E}
  3. {E}\{\text{E}\}{E} (correct answer)
  4. {D,E}\{\text{D},\text{E}\}{D,E}

Explanation: This question requires determining the intersection of events in a letter selection sample space. An event is a subset of the sample space S = {A,B,C,D,E}, which specifies the possible letter outcomes. A ∩ B denotes outcomes that are both in A (vowel) and B (after C), phrased as 'A and B.' The correct set {E} is accurate because E is a vowel and comes after C, directly matching an outcome in S. A tempting choice like {A,E} overlooks the 'and' requirement, confusing intersection with just A (vowels). Translate 'and' to intersection, identify outcomes satisfying both from S, and list them exactly. This method ensures the event reflects S's listings without extraneous assumptions.

Question 9

Based on the sample space shown for rolling one standard die, S={1,2,3,4,5,6}S=\{1,2,3,4,5,6\}S={1,2,3,4,5,6}, let event AAA be “roll a number greater than 4.” Which set represents AcA^cAc (not A)?

  1. SSS
  2. {1,2,3,4}\{1,2,3,4\}{1,2,3,4} (correct answer)
  3. {5,6}\{5,6\}{5,6}
  4. {2,4,6}\{2,4,6\}{2,4,6}

Explanation: This question involves finding the complement of an event in a sample space. An event is a subset of the sample space, which lists all possible outcomes of the experiment. The complement A^c means the outcomes that do not satisfy event A, or in plain language, 'not A.' The correct answer {1,2,3,4} matches because these are the numbers not greater than 4, for example, 4 is ≤4 (in A^c), while 5 is >4 (not in A^c). A tempting distractor is {5,6}, which is A itself, failing to invert the condition (misconception: confusing complement with the event). To handle similar problems, translate words like 'not' to complement, then list outcomes from S that do not fit the description exactly. Remember, events must precisely match the outcomes listed in S.

Question 10

Using the outcomes listed for selecting one marble from a bag, S={Rs,Rl,Bs,Bl}S=\{R_s,R_l,B_s,B_l\}S={Rs​,Rl​,Bs​,Bl​} where RRR=red, BBB=blue, sss=small, lll=large. Let event AAA be “the marble is red,” and let event BBB be “the marble is large.” Which expression represents A∪BA\cup BA∪B (A or B)?

  1. {Bs}\{B_s\}{Bs​}
  2. {Rs,Rl}\{R_s,R_l\}{Rs​,Rl​}
  3. {Rl}\{R_l\}{Rl​}
  4. {Rs,Rl,Bl}\{R_s,R_l,B_l\}{Rs​,Rl​,Bl​} (correct answer)

Explanation: This question involves finding the union of two events in a sample space. An event is a subset of the sample space, which lists all possible outcomes of the experiment. The union A ∪ B means the outcomes that satisfy event A or event B or both, or in plain language, 'A or B.' The correct answer {R_s,R_l,B_l} matches because these include all red or large marbles, for example, R_s is red (in A but not B), while B_l is large (in B but not A). A tempting distractor is {R_s,R_l}, which is just A, failing to include outcomes only in B (misconception: confusing union with intersection). To handle similar problems, translate words like 'either' or 'or' to union, then list outcomes from S that fit at least one description exactly. Remember, events must precisely match the outcomes listed in S.

Question 11

Based on the sample space shown for choosing one ordered pair, S={(1,1),(1,2),(2,1),(2,2)}S=\{(1,1),(1,2),(2,1),(2,2)\}S={(1,1),(1,2),(2,1),(2,2)}, let event AAA be “the sum of the two numbers is 3,” and let event BBB be “the first number is 2.” Which expression represents A∪BA\cup BA∪B (A or B)?

  1. {(1,2),(2,1),(2,2)}\{(1,2),(2,1),(2,2)\}{(1,2),(2,1),(2,2)} (correct answer)
  2. {(2,1)}\{(2,1)\}{(2,1)}
  3. {(1,2),(2,1)}\{(1,2),(2,1)\}{(1,2),(2,1)}
  4. {(1,1),(1,2),(2,1)}\{(1,1),(1,2),(2,1)\}{(1,1),(1,2),(2,1)}

Explanation: This question involves finding the union of two events in a sample space. An event is a subset of the sample space, which lists all possible outcomes of the experiment. The union A ∪ B means the outcomes that satisfy event A or event B or both, or in plain language, 'A or B.' The correct answer {(1,2),(2,1),(2,2)} matches because these have sum 3 or first number 2, for example, (1,2) sums to 3 (in A but not B), while (2,2) has first 2 (in B but not A). A tempting distractor is {(1,2),(2,1)}, which is just A, failing to include outcomes only in B (misconception: confusing union with intersection). To handle similar problems, translate words like 'either' or 'or' to union, then list outcomes from S that fit at least one description exactly. Remember, events must precisely match the outcomes listed in S.

Question 12

Using the outcomes listed for a spinner with 6 equal sections labeled S={R1,R2,B1,B2,G1,G2}S=\{R1,R2,B1,B2,G1,G2\}S={R1,R2,B1,B2,G1,G2} (R=red, B=blue, G=green), define event AAA as “the outcome is red” and event BBB as “the outcome has number 2.” Which expression represents A∪BA\cup BA∪B (A or B)?

  1. {R1,R2,B2,G2}\{R1,R2,B2,G2\}{R1,R2,B2,G2} (correct answer)
  2. {R1,R2}\{R1,R2\}{R1,R2}
  3. {B1,G1}\{B1,G1\}{B1,G1}
  4. {R2}\{R2\}{R2}

Explanation: This question involves finding the union of two events in a sample space. An event is a subset of the sample space, which lists all possible outcomes of the experiment. The union A ∪ B means the outcomes that satisfy event A or event B or both, or in plain language, 'A or B.' The correct answer {R1,R2,B2,G2} matches because these include all red outcomes and all with number 2, for example, R1 is red (in A but not B), while B2 has 2 (in B but not A). A tempting distractor is {R2}, which is the intersection, failing to include outcomes in only one event (misconception: confusing union with intersection). To handle similar problems, translate words like 'either' or 'or' to union, then list outcomes from S that fit at least one description exactly. Remember, events must precisely match the outcomes listed in S.

Question 13

Based on the sample space shown for choosing one letter, S={A,B,C,D,E,F}S=\{A,B,C,D,E,F\}S={A,B,C,D,E,F}, define event A={x∈S∣x is a vowel}A=\{x\in S\mid x\text{ is a vowel}\}A={x∈S∣x is a vowel}. Which set of outcomes represents event AAA?

  1. {A,B,E}\{A,B,E\}{A,B,E}
  2. {E}\{E\}{E}
  3. {B,C,D,F}\{B,C,D,F\}{B,C,D,F}
  4. {A,E}\{A,E\}{A,E} (correct answer)

Explanation: This question involves identifying an event as a subset of the sample space. An event is a subset of the sample space, which lists all possible outcomes of the experiment. Here, no operation like union or intersection is needed; it's directly listing the subset for A. The correct answer {A,E} matches because these are the vowels in S, for example, A is a vowel, while B is a consonant (not in A). A tempting distractor is {A,B,E}, which includes extra non-vowels, failing to stick to the definition (misconception: overincluding based on partial matches like starting letter). To handle similar problems, translate the event words to the matching subset, then list outcomes from S that fit the description exactly. Remember, events must precisely match the outcomes listed in S.

Question 14

Using the outcomes listed, a student randomly selects one card from a set labeled S={1R,1B,2R,2B,3R,3B}S=\{1R,1B,2R,2B,3R,3B\}S={1R,1B,2R,2B,3R,3B} (number 1–3 and color R=red or B=blue). Let event AAA be “the card is blue,” and let event BBB be “the number is 2 or 3.” Which expression represents A∩BA\cap BA∩B (A and B)?

  1. {2B,3B}\{2B,3B\}{2B,3B} (correct answer)
  2. {1B,2B,3B}\{1B,2B,3B\}{1B,2B,3B}
  3. {2B}\{2B\}{2B}
  4. {2R,2B,3R,3B}\{2R,2B,3R,3B\}{2R,2B,3R,3B}

Explanation: This question involves finding the intersection of two events in a sample space. An event is a subset of the sample space, which lists all possible outcomes of the experiment. The intersection A ∩ B means the outcomes that satisfy both event A and event B simultaneously, or in plain language, 'A and B.' The correct answer {2B,3B} matches because these are blue cards with number 2 or 3, for example, 2B is blue and 2 (satisfies both), while 2R is 2 but red (not both). A tempting distractor is {2R,2B,3R,3B}, which is just B, failing to require both conditions (misconception: confusing intersection with union or single event). To handle similar problems, translate words like 'both' or 'and' to intersection, then list outcomes from S that fit both descriptions exactly. Remember, events must precisely match the outcomes listed in S.

Question 15

Using the outcomes listed in S={small,medium,large}S=\{\text{small},\text{medium},\text{large}\}S={small,medium,large} for selecting one T-shirt size, event AAA is “the size is small” and event BBB is “the size is large.” Which set represents A∪BA\cup BA∪B (A or B)?

  1. {small}\{\text{small}\}{small}
  2. {medium}\{\text{medium}\}{medium}
  3. {small,large}\{\text{small},\text{large}\}{small,large} (correct answer)
  4. SSS

Explanation: This question asks for the union of two events, which includes all outcomes in at least one of the events. An event is a subset of the sample space containing outcomes that satisfy a given condition. The union A∪B represents sizes that are small OR large, meaning any outcome that is either small or large (or both, though that's impossible here). Since A is "small" which gives {small} and B is "large" which gives {large}, their union A∪B is {small,large}. A common error would be thinking "or" means choosing between events rather than combining their outcomes. The strategy for unions is to list all outcomes from both events without repetition.

Question 16

According to the sample space S={1,2,3,4,5,6,7,8}S=\{1,2,3,4,5,6,7,8\}S={1,2,3,4,5,6,7,8} for selecting one card labeled 1 through 8, let event AAA be “the number is even” and event B={x∈S∣x>5}B=\{x\in S\mid x>5\}B={x∈S∣x>5}. Which expression represents A∩BA\cap BA∩B (A and B)?

  1. {6,8}\{6,8\}{6,8} (correct answer)
  2. SSS
  3. {6,7,8}\{6,7,8\}{6,7,8}
  4. {2,4,6,8}\{2,4,6,8\}{2,4,6,8}

Explanation: This question asks for the intersection of two events, which means finding outcomes that belong to both events simultaneously. An event is a subset of the sample space containing outcomes that satisfy a given condition. The intersection A∩BA \cap BA∩B represents outcomes that are both even AND greater than 5, which translates to finding numbers in SSS that satisfy both conditions at once. Looking at S={1,2,3,4,5,6,7,8}S=\{1,2,3,4,5,6,7,8\}S={1,2,3,4,5,6,7,8}, the even numbers are \ {2,4,6,8\} and numbers greater than 5 are \ {6,7,8\}, so their intersection contains only \ {6,8\}. A common mistake is confusing intersection with union, which would give all outcomes in either set rather than just those in both. The strategy is to first list outcomes for each event separately, then identify which outcomes appear in both lists.

Question 17

According to the sample space S={10,11,12,13,14,15}S=\{10,11,12,13,14,15\}S={10,11,12,13,14,15} for selecting one integer, let event AAA be “the number is a multiple of 3” and event BBB be “the number is even.” Which expression represents A∪BA\cup BA∪B (A or B)?

  1. {10,11,12,13,14,15}\{10,11,12,13,14,15\}{10,11,12,13,14,15}
  2. {10,12,14,15}\{10,12,14,15\}{10,12,14,15} (correct answer)
  3. {10,12,14}\{10,12,14\}{10,12,14}
  4. {12}\{12\}{12}

Explanation: This question asks for the union of two events, meaning all outcomes in at least one event. An event is a subset of the sample space containing outcomes that meet a condition. The union A∪B represents numbers that are multiples of 3 OR even numbers, including any outcome satisfying either property. From S={10,11,12,13,14,15}, event A (multiples of 3) contains {12,15} and event B (even numbers) contains {10,12,14}, so their union is {10,12,14,15}. A common mistake is finding only the intersection {12}, which would be numbers that are both multiples of 3 AND even. To solve union problems, combine all outcomes from both events, counting shared outcomes only once.

Question 18

Based on the sample space shown, S={(1,1),(1,2),(1,3),(2,1),(2,2),(2,3)}S=\{(1,1),(1,2),(1,3),(2,1),(2,2),(2,3)\}S={(1,1),(1,2),(1,3),(2,1),(2,2),(2,3)} for rolling a 2-sided die (1–2) and a 3-sided die (1–3) and recording an ordered pair (first, second), let event AAA be “the sum is 4” and event BBB be “the first number is 2.” Which set of outcomes represents A∩BA\cap BA∩B (A and B)?

  1. {(1,3)}\{(1,3)\}{(1,3)}
  2. {(2,2)}\{(2,2)\}{(2,2)} (correct answer)
  3. {(1,3),(2,2)}\{(1,3),(2,2)\}{(1,3),(2,2)}
  4. {(2,1),(2,2),(2,3)}\{(2,1),(2,2),(2,3)\}{(2,1),(2,2),(2,3)}

Explanation: This question asks for the intersection of two events, requiring outcomes that satisfy both conditions simultaneously. An event is a subset of the sample space containing outcomes meeting specific criteria. The intersection A∩B means outcomes where the sum is 4 AND the first number is 2, so we need ordered pairs satisfying both conditions at once. Event A (sum is 4) contains {(1,3),(2,2)} since 1+3=4 and 2+2=4, while event B (first number is 2) contains {(2,1),(2,2),(2,3)}, so their intersection is just {(2,2)}. A typical error is listing all outcomes from either event (union) rather than only those in both. The strategy is to identify each event's outcomes separately, then find which appear in both lists.

Question 19

According to S={H,T}S=\{\text{H},\text{T}\}S={H,T} for flipping one coin, let event AAA be “the outcome is heads” and event BBB be “the outcome is tails.” Which expression represents A∩BA\cap BA∩B (A and B)?

  1. {H}\{\text{H}\}{H}
  2. {T}\{\text{T}\}{T}
  3. {H,T}\{\text{H},\text{T}\}{H,T}
  4. ∅\varnothing∅ (correct answer)

Explanation: This question asks for the intersection of two events, requiring outcomes that belong to both events simultaneously. An event is a subset of the sample space containing outcomes that meet specific criteria. The intersection A∩B represents outcomes that are both heads AND tails, which is impossible for a single coin flip - an outcome cannot be both H and T at the same time. Since no outcome in S={H,T} can satisfy both conditions simultaneously, the intersection is the empty set ∅. A common error is confusing "and" with "or" and answering {H,T}, which would be the union. The key insight is that intersection requires outcomes to satisfy all conditions at once, which may result in an empty set when conditions are mutually exclusive.

Question 20

According to S={Mon,Tue,Wed,Thu,Fri,Sat,Sun}S=\{\text{Mon},\text{Tue},\text{Wed},\text{Thu},\text{Fri},\text{Sat},\text{Sun}\}S={Mon,Tue,Wed,Thu,Fri,Sat,Sun}, one day is chosen at random. Event A={x∈S∣x is a weekday}A=\{x\in S\mid x\text{ is a weekday}\}A={x∈S∣x is a weekday}. Which set of outcomes represents event AAA?

  1. SSS
  2. {Mon,Wed,Fri,Sun}\{\text{Mon},\text{Wed},\text{Fri},\text{Sun}\}{Mon,Wed,Fri,Sun}
  3. {Mon,Tue,Wed,Thu,Fri}\{\text{Mon},\text{Tue},\text{Wed},\text{Thu},\text{Fri}\}{Mon,Tue,Wed,Thu,Fri} (correct answer)
  4. {Sat,Sun}\{\text{Sat},\text{Sun}\}{Sat,Sun}

Explanation: This question asks for the description of an event as a subset of the sample space. An event is a subset of the sample space, which lists all possible outcomes. Here, event A is directly defined as the weekdays, without needing operations like and/or/not. The correct answer {Mon, Tue, Wed, Thu, Fri} matches because these are the outcomes in S that are weekdays, for example, Mon is a weekday and listed in S. A tempting distractor is {Sat, Sun}, which are the weekends, failing because it lists non-weekdays, confusing the event with its complement. To solve similar problems, translate the event description to a subset, then list outcomes from S that match the condition exactly as described. Always ensure the outcomes match those listed in S precisely.