Design Simulations for Compound Events

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7th Grade Math › Design Simulations for Compound Events

Questions 1 - 10
1

A game booth works like this: You roll a fair die twice. You win a prize if both rolls are even (2, 4, or 6).

Which simulation would correctly estimate the probability of winning?

Roll a die once per trial and count a win if the roll is even; repeat 100 trials.

Flip a coin twice per trial and count a win if both are heads; repeat 100 trials.

Roll a die twice total, and if you get at least one even, estimate the probability as $1/2$.

Roll a die twice per trial and count a win if both rolls are even; repeat 100 trials and estimate $P(\text{win})$ as wins/100.

Explanation

This question tests designing simulations using random devices to estimate compound event probabilities through trials and frequency, for winning by rolling two even numbers on a die (P(even)=0.5). Design: (1) identify the event as two independent rolls both even, (2) use a die (even on 2,4,6 for P=3/6=0.5), (3) define success as both even in two rolls per trial, (4) perform many trials (e.g., 100), (5) estimate P as wins over trials. Example: roll a die twice per trial, check if both are even, repeat 100 times, and calculate the proportion of wins to estimate the 0.25 probability. Choice B is correct, using the die to match the game, compounding two rolls per trial, defining the both-even success, and running 100 trials. Errors include single rolls, mismatched devices or probabilities, or insufficient trials like only two total rolls. In designing, examine the event structure, choose a matching random device, map outcomes properly, specify trial numbers, and outline frequency estimation. Run simulations by randomizing actions, recording results, counting successes, and computing estimates; avoid mismatches, low trials, incorrect mappings, or errors in calculation.

2

A science club says a homemade rocket launches successfully about 60% of the time. You want to simulate the compound event: in 3 launches, the rocket succeeds exactly 2 times. Which plan is a complete and correct simulation?

Use a 10-section spinner with 6 sections labeled Success and 4 labeled Fail. Spin once and use that to decide the outcome for all 3 launches in the trial. Repeat 100 trials.

Flip a coin 3 times; heads = Success. Repeat 100 trials and estimate $P$ as successes/100.

Use a die; 1–2 = Success and 3–6 = Fail. Do 5 trials and estimate $P$ as successes/5.

Use a 10-section spinner with 6 sections labeled Success and 4 labeled Fail. Spin 3 times per trial, count trials with exactly 2 Successes, repeat 100 trials, and estimate $P$ as successes/100.

Explanation

This question tests designing simulations using random devices to estimate compound event probabilities through trials and frequency. A proper design involves: (1) identifying the event probability, here approximately 0.6 for successful launch, (2) choosing a device that matches this probability, such as a 10-section spinner with 6 sections labeled Success (P=6/10=0.6), (3) defining success as getting exactly 2 Successes in 3 spins per trial, (4) running multiple trials like 100, and (5) estimating P as the number of successful trials divided by 100. For example, in simulating 60% success rate, use a 10-spinner with 6 marked Success, perform 100 trials of 3 spins each, count trials with exactly 2 Successes, and estimate P as that count over 100. The correct design is choice A, which uses a 10-section spinner with 6 Success and 4 Fail, spins 3 times per trial to check for exactly 2 Successes, and estimates over 100 trials. Errors in other choices include improper single spin for all launches in B, mismatched coin (P=0.5) in C, and incorrect mapping (P=2/6≈0.333) with too few trials in D. When designing such simulations, first analyze the compound event and its base probability, then select a device that closely matches that probability and map outcomes clearly to define success for the compound condition. Finally, specify a sufficient number of trials, run them by randomizing, recording outcomes, counting successes, and calculating the frequency as the estimate, while avoiding common mistakes like probability mismatches or insufficient trials for reliable estimates.

3

A basketball player makes a free throw with probability about $0.7$. You want to simulate the compound event: the player takes 3 free throws and makes at least 2. Which simulation plan is best?

Roll one die once (1–4 = Make). If it’s 1–4, count it as “at least 2 makes.” Repeat 100 trials.

Flip a coin 3 times (heads = Make). Record whether at least 2 heads occur. Repeat 10 trials.

Use a 10-section spinner with 7 sections labeled Make and 3 labeled Miss. For each trial, spin 3 times and record whether at least 2 are Make. Repeat 100 trials and estimate the probability by successes/trials.

Spin a 10-section spinner once (7 Make, 3 Miss). If it lands on Make, count it as “at least 2 makes.” Repeat 100 trials.

Explanation

This question tests designing simulations using random devices to estimate compound event probabilities through trials and frequency, specifically for making at least 2 out of 3 free throws with P(make) ≈ 0.7. A good design includes: (1) identifying the binomial event with P=0.7, (2) selecting a device like a 10-section spinner with 7 sections marked Make (P=7/10=0.7), (3) defining success as at least 2 Makes in 3 spins per trial, (4) conducting many trials (e.g., 100), (5) estimating P as successes over trials. For instance, using a 10-section spinner (7 Make, 3 Miss), spin 3 times per trial, check for at least 2 Makes, repeat 100 times, and compute the proportion of successes to approximate the probability. The best choice is A, as it correctly matches P=0.7, simulates 3 attempts per trial, defines the compound success, and uses 100 trials. Errors to avoid include wrong probabilities (e.g., coin at 0.5 or die at 4/6≈0.67), oversimplifying to single actions without compounding, or too few trials like only 10. In designing, analyze the event's components, choose a matching device, map outcomes to successes, set sufficient trials, and outline estimation via relative frequency. Execute by randomizing each spin or roll, recording per-trial results, counting successes, and calculating the ratio; common pitfalls are probability mismatches, insufficient repetitions, incorrect success mappings, or miscalculations.

4

A cafeteria line has a $40%$ chance that the next student chooses pizza. About how many students would you expect to check before you have found 10 pizza choices? (Use estimation.)

About 10 students

About 40 students

About 25 students

About 4 students

Explanation

This question tests designing simulations using random devices to estimate compound event probabilities through trials and frequency. The design involves: (1) identifying the event as choosing pizza (P=0.4), (2) choosing a device matching P, (3) defining success as pizza, (4) running trials until k successes, (5) estimating expected trials as k/P. For example, for 10 pizza choices at P=0.4, expected students ≈10/0.4=25; in simulation, you might spin until 10 successes and count total spins. The correct estimate is option C, about 25 students, using the formula for expected value in geometric distribution (trials to k successes ≈k/P). Errors in other options include wrong calculations like 100.4=4 (A), 10 (B), or 0.4100=40 (D). When designing: (1) analyze the waiting-time event, (2) select device, (3) map success, (4) simulate until k, (5) use k/P for expectation. Mistakes include confusing probability with expectation or arithmetic errors.

5

A student uses a 10-section spinner (4 sections labeled A, 6 labeled not A) to simulate the chance a randomly chosen donor has blood type A. After 80 spins, the spinner landed on A 28 times. What is the estimated probability of type A based on the simulation?

$\frac{80}{28}\approx 2.86$

$\frac{28}{80}=0.35$

$\frac{4}{10}=0.25$

$\frac{28}{10}=2.8$

Explanation

This question tests designing simulations using random devices to estimate compound event probabilities through trials and frequency. The design involves: (1) identifying the event as type A (P via 4/10 spinner), (2) choosing the spinner, (3) defining success as A, (4) running 80 spins, (5) estimating as 28/80=0.35. For example, 28 A's in 80 gives 0.35, close to 0.4; expected A's in 80 is 32. The correct estimate is option A, 28/80=0.35. Errors include inverting (80/28), wrong denominator (28/10), or unrelated fraction (4/10). When designing: (1) analyze event, (2) select device, (3) map, (4) run trials, (5) calculate ratio. Running: spin, record, count, divide; mistakes are arithmetic errors in fractions.

6

A class simulates the compound event: in 4 tries, a student gets at least 1 correct answer by guessing. Each guess has probability $0.4$ of being correct. They run 100 trials, and 82 trials had at least 1 correct answer. Based on the simulation, what is the estimated probability of the compound event?

$0.40$

$1.22$

$0.18$

$0.82$

Explanation

This question tests designing simulations using random devices to estimate compound event probabilities through trials and frequency. A proper design involves: (1) identifying the event probability, here 0.4 for a correct guess, (2) choosing a matching device, (3) defining success as at least 1 correct in 4 attempts per trial, (4) running trials like 100, and (5) estimating P as successes over total trials, such as 82/100=0.82. For example, in simulating P=0.4 success, run 100 trials of 4 attempts each, count trials with at least 1 success, and if 82, estimate P=0.82. The correct estimate is choice C, which is 82/100=0.82, directly from the simulation results. Errors in other choices include incorrect calculations like 0.18 (perhaps 1-0.82) in A, the base P=0.4 in B, and invalid 1.22 in D. When designing such simulations, first analyze the compound event and its base probability, then select a device that matches it and map outcomes to define success. Finally, run sufficient trials by randomizing, record and count successes, calculate the estimate as frequency, and avoid mistakes like arithmetic errors in estimation.

7

A student runs a simulation for the compound event: spin a 10-section spinner twice; event occurs if both spins land on a red section. The spinner has 4 red sections and 6 blue sections.

After 120 trials, the event happened 18 times. What is the estimated probability of the event?

$0.40$

$0.18$

$0.15$

$0.85$

Explanation

This question tests designing simulations using random devices to estimate compound event probabilities through trials and frequency, here computing the estimate from given results for both spins red on a spinner with P(red)=4/10=0.4. After running trials: with 18 occurrences in 120 trials, estimate P=18/120=0.15, approximating the theoretical $(0.4)^2$=0.16. Example: in a simulation of two spins with 4 red sections, if the both-red event happens 18 times in 120, the relative frequency is 18/120=0.15. Choice A is correct, as 18 divided by 120 equals 0.15. Errors might include wrong calculations like 18/100=0.18, using single P=0.4, or adding to 0.85. In estimation, after trials, count successes, divide by total trials for the probability. Ensure accurate arithmetic; common pitfalls are division mistakes or misinterpreting the compound event.

8

A school nurse knows about $40%$ of students have blood type A. The nurse wants to simulate the compound event: selecting 10 donors and counting how many are type A. Which simulation design is best?

(Your design should include a random device, how outcomes match blood types, and enough trials to estimate the probability.)

Roll a die once for each donor (1–4 = type A). Do 10 rolls total and use the result as the estimate.

Pick 10 students you know and count how many have type A. Repeat until you feel confident.

Use a 10-section spinner with 4 sections labeled A and 6 labeled not A. For each trial, spin 10 times (one per donor), record how many A’s occur, and repeat for 100 trials.

Flip a coin once for each donor (heads = type A). Do 10 flips total and use the result as the estimate.

Explanation

This question tests designing simulations using random devices to estimate compound event probabilities through trials and frequency, focusing on simulating the count of type A blood donors out of 10 with P(type A) ≈ 0.4. A proper design involves: (1) identifying the event as binomial with P=0.4, (2) choosing a device like a 10-section spinner with 4 sections labeled A (P=4/10=0.4), (3) defining each trial as 10 spins and counting A's, (4) running multiple trials (e.g., 100), (5) using the distribution of counts to understand the event. For example, with a 10-section spinner (4 A, 6 not A), perform 100 trials of 10 spins each, recording the number of A's per trial to estimate the probability distribution of the count. The correct design is choice B, as it matches P=0.4, simulates 10 donors per trial by spinning 10 times, and uses 100 trials for reliability. Common errors include mismatched probabilities (e.g., coin at 0.5 or die at 4/6≈0.67), insufficient trials (e.g., only 10 total actions), or non-random methods like picking known students. When designing such simulations, first analyze the compound event's structure, then select a device that matches the individual probabilities, map outcomes to event components, specify enough trials for accuracy, and describe how to estimate frequencies or distributions. To run the simulation, ensure randomization in each action, record results per trial, count relevant outcomes, and calculate relative frequencies; avoid mistakes like probability mismatches, too few trials, unclear success definitions, or arithmetic errors in estimation.

9

A student wants to simulate the compound event: choose 4 students and at least 1 has a birthday in March. Assume the probability a randomly chosen student has a March birthday is about $\frac{1}{12}\approx 0.083$. Which device and mapping is the best simple approximation?

Roll a die; 1 = March birthday, 2–6 = not March birthday.

Use a 12-section spinner; 1 section = March birthday and 11 sections = not March birthday.

Flip a coin; heads = March birthday.

Use a 10-section spinner; 4 sections = March birthday and 6 sections = not March birthday.

Explanation

This question tests designing simulations using random devices to estimate compound event probabilities through trials and frequency. A proper design involves: (1) identifying the event probability, here approximately 1/12≈0.083 for March birthday, (2) choosing a device that matches this probability, such as a 12-section spinner with 1 section labeled March (P=1/12≈0.083), (3) defining success as at least 1 March in 4 spins per trial, (4) running multiple trials, and (5) estimating P as the frequency of successes. For example, in simulating 1/12 chance of March birthday, use a 12-spinner with 1 marked March, perform trials of 4 spins each, count those with at least 1 March, and estimate P over many trials. The correct mapping is choice D, which uses a 12-section spinner with 1 March and 11 not, accurately representing P≈0.083 for each selection. Errors in other choices include mismatched probabilities like coin (P=0.5) in A, die with P=1/6≈0.167 in B, and 10-spinner with P=4/10=0.4 in C. When designing such simulations, first analyze the compound event and its base probability, then select a device that closely matches that probability and map outcomes clearly to define success for the compound condition. Finally, specify a sufficient number of trials, run them by randomizing, recording outcomes, counting successes, and calculating the frequency as the estimate, while avoiding common mistakes like probability mismatches or insufficient trials for reliable estimates.

10

A factory estimates that about $10%$ of its pens are defective. You want to simulate the compound event: checking 5 pens and finding at least 1 defective. Which choice is the best simulation design using simple random devices?

Use a 10-section spinner with 1 section labeled Defective and 9 labeled OK. For each trial, spin 5 times and record whether at least 1 Defective occurs. Repeat 100 trials and estimate with successes/trials.

Choose 5 pens from your pencil case and see if any seem defective. Use that as the estimate.

Flip a coin 5 times (heads = defective). Repeat 100 trials.

Roll a die 5 times (1 = defective). Do this once and use that single result as the probability.

Explanation

This question tests designing simulations using random devices to estimate compound event probabilities through trials and frequency, for finding at least 1 defective in 5 pens with P(defective) ≈ 0.1. Design steps: (1) recognize the binomial setup with P=0.1, (2) use a device like a 10-section spinner with 1 Defective (P=1/10=0.1), (3) define success as at least 1 Defective in 5 spins per trial, (4) run ample trials (e.g., 100), (5) estimate P as successes divided by trials. Example: with a 10-section spinner (1 Defective, 9 OK), spin 5 times per trial, note if any Defective, repeat 100 trials, and find the success rate for the probability estimate. Choice B is correct, matching P=0.1, compounding 5 checks per trial, specifying the at-least-1 condition, and using 100 trials. Typical mistakes are incorrect probabilities (e.g., coin at 0.5 or die at 1/6≈0.167), single-run without repetition, or non-random observations. For effective designing, break down the event, pick a probability-matching device, map to compound outcomes, determine trial count, and explain frequency-based estimation. Run by ensuring random outcomes, tracking per trial, tallying successes, and computing ratios; steer clear of mismatches, low trial numbers, mapping flaws, or arithmetic issues.

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