Describing Events in Sample Spaces

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Statistics › Describing Events in Sample Spaces

Questions 1 - 10
1

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

${2,4,6,8}$

${6,8}$

${7}$

${1,2,3,4,5,6,7,8}$

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.

2

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

${\text{banana},\text{carrot}}$

${\text{apple},\text{banana},\text{dates}}$

${\text{carrot}}$

${\text{banana}}$

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.

3

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

${\text{fish}}$

${\text{fish},\text{bird}}$

${\text{cat},\text{dog},\text{fish},\text{bird}}$

${\text{cat},\text{dog}}$

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.

4

Based on the sample space $S={(1,1),(1,2),(1,3),(2,1),(2,2),(2,3)}$ for rolling a 2-sided die (values 1–2) and a 3-sided die (values 1–3) and recording (first, second), let event $A$ be “the sum is 4” and event $B$ be “the first number is 2.” Which set represents $A\cup B$ (A or B)?

${(2,2)}$

${(1,1),(1,2),(1,3)}$

${(1,3),(2,2),(2,1),(2,3)}$

${(2,1),(2,2),(2,3)}$

Explanation

This question seeks the union of events in a two-die roll sample space. An event is a subset of the sample space S = {(1,1),(1,2),(1,3),(2,1),(2,2),(2,3)}, showing paired outcomes. A ∪ B means outcomes in A (sum 4) or B (first is 2), or 'A or B' plainly. The correct set {(1,3),(2,2),(2,1),(2,3)} matches because (1,3) sums to 4 in A, and (2,1),(2,2),(2,3) have first 2 in B, all from S. A distractor like {(2,1),(2,2),(2,3)} misses (1,3), confusing union with only B. Translate 'or' to union, combine unique outcomes from both events in S. Focus on S's exact outcome formats for correct event depiction.

5

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

${1,2,3}$

${3,4,5,6}$

${1,3,5}$

${4,5,6}$

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.

6

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

${(H,T)}$

${(H,H),(H,T),(T,H)}$

${(H,H),(H,T),(T,H),(T,T)}$

${(H,T),(T,H)}$

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.

7

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

${\text{M},\text{T},\text{W},\text{Th},\text{F}}$

${\text{M},\text{W},\text{F}}$

${\text{Th}}$

${\text{T},\text{Th}}$

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.

8

Using the outcomes listed in $S={\text{small},\text{medium},\text{large}}$ for randomly selecting one shirt size, event $A$ is “not medium.” Which set represents $A$?

${\text{small},\text{medium},\text{large}}$

${\text{small},\text{large}}$

${\text{small}}$

${\text{medium}}$

Explanation

This question involves defining an event that is essentially a complement in a shirt size sample space. An event is a subset of the sample space S = {small,medium,large}, outlining the possible sizes. Event A as 'not medium' means all outcomes excluding medium, or 'not' in simple language. The correct set {small,large} fits because small and large are not medium, both explicitly from S. A distractor such as {small,medium,large} errs by including everything, confusing the event with the full S instead of its complement. Convert 'not' to complement, remove the specified outcome from S, and list the rest as they appear. This approach guarantees the event matches S's exact listings accurately.

9

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

${B1,B2,B3}$

${R1,R2,R3}$

${R1,B1}$

${R1,R2,R3,B1,B2,B3}$

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.

10

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

${\text{A},\text{E}}$

${\text{D},\text{E}}$

${\text{A},\text{B},\text{C},\text{D},\text{E}}$

${\text{E}}$

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.

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