Develop Non-Uniform Probability Models

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7th Grade Math › Develop Non-Uniform Probability Models

Questions 1 - 10
1

A spinner has four sections labeled A, B, C, and D. After 200 spins, the results were: A 70, B 50, C 60, D 20. Which probability model best matches the results?​

$P(A)=0.30,;P(B)=0.35,;P(C)=0.25,;P(D)=0.10$

$P(A)=\frac{70}{200}=0.35,;P(B)=\frac{50}{200}=0.25,;P(C)=\frac{60}{200}=0.30,;P(D)=\frac{20}{200}=0.10$

$P(A)=\frac{1}{4},;P(B)=\frac{1}{4},;P(C)=\frac{1}{4},;P(D)=\frac{1}{4}$

$P(A)=0.70,;P(B)=0.50,;P(C)=0.60,;P(D)=0.20$

Explanation

This question tests developing a non-uniform model from spinner frequencies over 200 spins, using relative frequencies. Non-uniform: unequal; develop by observing A70, B50, C60, D20, calculating 70/200=0.35, etc., sum=1. For example, P(A)=0.35, P(B)=0.25, P(C)=0.30, P(D)=0.10, matching data. The correct model is B, with accurate relative frequencies. Errors: dividing by 100 in A, uniform in C, swapping in D. Developing: (1) collect, (2) calculate relative, (3) assign, (4) verify sum=1. Non-uniform from sections; mistakes: wrong denominator or assuming equal.

2

A teacher surveyed 100 students about their favorite after-school activity: Sports 38, Video games 34, Reading 28. A probability model is made from the survey. In a new survey of 50 students, 21 chose Sports. Which conclusion is best?​

The model predicts about $0.38\times 50=38$ Sports choices, so 21 is too small.

The model must be uniform because there are 3 activities.

The model predicts about $0.38\times 50=19$ Sports choices, and 21 is close, so the model seems reasonable.

The model predicts exactly 19 Sports choices, so 21 means the model is incorrect.

Explanation

This question tests using a non-uniform model from student activity frequencies to predict in a new survey and comparing to observations. Non-uniform: unequal; model from 100 students, P(sports)=38/100=0.38, predict 0.38×50=19, observe 21 close. For example, expected ≈19 sports, 21 is reasonably close, model fits. The correct conclusion is A, assessing fit with approximation. Errors: exact expectation in B, miscalculation in C (38 instead of 19), uniform assumption in D. Comparing: expected P×n vs. observed, assess fit; non-uniform from preferences. Mistakes: demanding exactness or math errors.

3

A music app tracked what a student listened to on 60 days: Pop 27 days, Rap 21 days, Other 12 days. Using a probability model based on these frequencies, what is $P(\text{Pop})$?​​

$\frac{1}{3}\approx 0.33$

$\frac{27}{60}=0.27$

$\frac{60}{27}\approx 2.22$

$\frac{27}{60}=0.45$

Explanation

This question tests developing a non-uniform probability model from observed frequencies to estimate a specific probability. A non-uniform model means outcomes are not equally likely, developed by observing frequencies (60 days: pop 27, rap 21, other 12), calculating relative frequencies (27/60=0.45, etc.), assigning probabilities, and verifying sum=1. For example, P(pop)=27/60=0.45 accurately reflects the data proportion for pop music. The correct estimate is choice A, showing the proper fraction and decimal. Common errors include incorrect decimals like B, inverting the fraction as in C, or assuming uniformity like D. To develop: (1) collect frequencies, (2) calculate relative frequencies, (3) assign probabilities, (4) verify sum=1. Non-uniform models capture preferences, and mistakes often involve calculation errors or not using the data.

4

A class uses a weighted spinner with three colors. In 100 practice spins, the results were: Red 45, Blue 30, Green 25. Which probability model best matches the practice data, and does it represent a uniform or non-uniform model?

$P(R)=0.45,;P(B)=0.30,;P(G)=0.25$; non-uniform

$P(R)=\frac{1}{3},;P(B)=\frac{1}{3},;P(G)=\frac{1}{3}$; uniform

$P(R)=0.45,;P(B)=0.25,;P(G)=0.30$; uniform

$P(R)=45,;P(B)=30,;P(G)=25$; non-uniform

Explanation

This question tests developing a non-uniform probability model from observed frequencies in spinner spins, assigning probabilities based on those frequencies, and identifying if the model is uniform or non-uniform. Non-uniform models have outcomes that are not equally likely, so to develop one, observe frequencies like 100 spins with red 45, blue 30, green 25, calculate relative frequencies as 45/100=0.45, 30/100=0.30, 25/100=0.25, assign these as probabilities, and verify they sum to 1. For example, P(red)=0.45, P(blue)=0.30, P(green)=0.25, and the sum is 1.00, which checks out, making it a valid non-uniform model since probabilities differ. The correct model is B, which uses these exact probabilities and correctly identifies it as non-uniform. Common errors include assuming a uniform model like A or D, using raw frequencies as in C, or swapping probabilities as in D. Developing a model involves (1) collecting frequencies, (2) calculating relative frequencies by dividing by total trials, (3) assigning them as probabilities, and (4) verifying the sum is 1. Non-uniform models arise from weighted or biased mechanisms, and mistakes often include assuming uniformity or not normalizing frequencies.

5

A game uses a biased die with faces 1–6. In 120 rolls, the results were: 1: 10, 2: 14, 3: 18, 4: 22, 5: 26, 6: 30. Which statement is true?

A model from the data gives $P(6)=30$, so the die appears uniform.

A model from the data gives $P(6)=\frac{30}{120}=0.25$, so the die appears non-uniform.

Because 6 happened the most, $P(6)=1$ and all other outcomes have probability 0.

The model is uniform because each outcome has probability $\frac{1}{6}$.

Explanation

This question tests developing a non-uniform model from biased die roll frequencies over 120 rolls and identifying non-uniformity. Non-uniform: not equal; develop by observing frequencies like 6:30, calculating P(6)=30/120=0.25, higher than 1/6≈0.167, indicating bias. For example, P(6)=0.25 vs. uniform 1/6, and increasing frequencies suggest non-uniform. The correct statement is B, recognizing the relative frequency shows non-uniformity. Errors: claiming uniform in A or C, using raw count in C, or extreme in D. Developing: (1) collect frequencies, (2) calculate relative, (3) assign, (4) verify sum=1; compare to uniform. Non-uniform from bias; mistakes: assuming fair or not calculating properly.

6

A music app tracked what a student listened to on 60 days: Pop 27 days, Rap 21 days, Other 12 days. Using a probability model based on these frequencies, what is $P(\text{Pop})$?

$\frac{27}{60}=0.27$

$\frac{60}{27}\approx 2.22$

$\frac{27}{60}=0.45$

$\frac{1}{3}\approx 0.33$

Explanation

This question tests developing a non-uniform probability model from observed frequencies to estimate a specific probability. A non-uniform model means outcomes are not equally likely, developed by observing frequencies (60 days: pop 27, rap 21, other 12), calculating relative frequencies (27/60=0.45, etc.), assigning probabilities, and verifying sum=1. For example, P(pop)=27/60=0.45 accurately reflects the data proportion for pop music. The correct estimate is choice A, showing the proper fraction and decimal. Common errors include incorrect decimals like B, inverting the fraction as in C, or assuming uniformity like D. To develop: (1) collect frequencies, (2) calculate relative frequencies, (3) assign probabilities, (4) verify sum=1. Non-uniform models capture preferences, and mistakes often involve calculation errors or not using the data.

7

A weather app looks at the last 30 days. It rained on 12 days and was sunny on 18 days. Based on these frequencies, what is the best probability model for tomorrow’s weather?

$P(\text{rain})=0.4,;P(\text{sun})=0.6$

$P(\text{rain})=12,;P(\text{sun})=18$

$P(\text{rain})=0.5,;P(\text{sun})=0.5$

$P(\text{rain})=0.6,;P(\text{sun})=0.4$

Explanation

This question tests developing a non-uniform probability model from observed frequencies, using it to predict the likelihood of weather outcomes. A non-uniform model means outcomes are not equally likely, developed by observing frequencies (30 days: rain 12, sun 18), calculating relative frequencies (12/30=0.4, 18/30=0.6), assigning these as probabilities, and verifying they sum to 1. For example, with 30 days showing rain on 12 and sun on 18, the probabilities are P(rain)=0.4, P(sun)=0.6, and they sum to 1.00, suitable for predicting tomorrow's weather. The correct model is choice A, which matches the relative frequencies from the data. Common errors include using raw counts like in B, swapping probabilities as in C, or assuming uniformity like D. To develop such a model: (1) collect outcome frequencies, (2) calculate relative frequencies by dividing by total observations, (3) assign these as probabilities, (4) verify they sum to 1. Using the model involves multiplying probabilities by future trials for predictions, and non-uniformity reflects real patterns like seasonal weather biases, with mistakes often from not normalizing frequencies or ignoring data for equal probabilities.

8

A cafeteria tracked which fruit students chose over 80 lunches: Apple 36, Banana 28, Orange 16. If the cafeteria uses a probability model based on this data, about how many banana choices should it expect in the next 50 lunches?​​

About $\left(\frac{36}{80}\right)\times 50=22.5$, so about 23 bananas

About $\left(\frac{28}{80}\right)\times 50=17.5$, so about 18 bananas

About $\left(\frac{16}{80}\right)\times 50=10$, so about 10 bananas

About $\left(\frac{28}{80}\right)\times 50=28$, so about 28 bananas

Explanation

This question tests developing a non-uniform probability model from observed frequencies and using it to predict future outcomes. A non-uniform model means outcomes are not equally likely, developed by observing frequencies (80 lunches: apple 36, banana 28, orange 16), calculating relative frequencies (28/80=0.35 for banana), assigning probabilities, verifying sum=1, then predicting (0.35×50=17.5, about 18). For example, the model predicts about 17.5 bananas in 50 lunches, rounding to about 18, based on the data. The correct prediction is choice A, with accurate calculation for bananas. Common errors include miscalculating the expected value like B, using wrong frequencies as in C or D. Developing: (1) collect frequencies, (2) calculate relative frequencies, (3) assign probabilities, (4) verify sum=1; using: predict P×n and round appropriately. Non-uniformity reflects choices, and mistakes include wrong proportions or exact expectations without approximation.

9

A cafeteria tracked which fruit students chose over 80 lunches: Apple 36, Banana 28, Orange 16. If the cafeteria uses a probability model based on this data, about how many banana choices should it expect in the next 50 lunches?

About $\left(\frac{36}{80}\right)\times 50=22.5$, so about 23 bananas

About $\left(\frac{28}{80}\right)\times 50=28$, so about 28 bananas

About $\left(\frac{28}{80}\right)\times 50=17.5$, so about 18 bananas

About $\left(\frac{16}{80}\right)\times 50=10$, so about 10 bananas

Explanation

This question tests developing a non-uniform probability model from observed frequencies and using it to predict future outcomes. A non-uniform model means outcomes are not equally likely, developed by observing frequencies (80 lunches: apple 36, banana 28, orange 16), calculating relative frequencies (28/80=0.35 for banana), assigning probabilities, verifying sum=1, then predicting (0.35×50=17.5, about 18). For example, the model predicts about 17.5 bananas in 50 lunches, rounding to about 18, based on the data. The correct prediction is choice A, with accurate calculation for bananas. Common errors include miscalculating the expected value like B, using wrong frequencies as in C or D. Developing: (1) collect frequencies, (2) calculate relative frequencies, (3) assign probabilities, (4) verify sum=1; using: predict P×n and round appropriately. Non-uniformity reflects choices, and mistakes include wrong proportions or exact expectations without approximation.

10

A game uses a spinner with outcomes A, B, and C. In 150 spins, the results were: A 60, B 45, C 45. A probability model based on this data is created. In the next 50 spins, the spinner lands on A 28 times. Which statement best describes how well the model matches the new results?

The model predicts about $\left(\frac{60}{150}\right)\times 50=30$ A’s, so 28 is close; the fit is very good.

The model must be uniform, so it predicts $\frac{1}{3}\times 50\approx 17$ A’s, and 28 is close.

The model predicts about $\left(\frac{60}{150}\right)\times 50=20$ A’s, so 28 is much higher; the fit is not very good.

The model predicts exactly 20 A’s, so any other number means the model is impossible.

Explanation

This question tests developing a non-uniform probability model from observed frequencies and comparing its predictions to new data for fit. A non-uniform model means outcomes are not equally likely, developed by observing frequencies (150 spins: A 60, B 45, C 45), calculating relative frequencies (60/150=0.4 for A), assigning probabilities, verifying sum=1, predicting (0.4×50=20), and assessing fit to observed (28 A's). For example, the model predicts about 20 A's in 50 spins, but observing 28 is much higher, suggesting the fit is not very good. The correct statement is choice A, accurately calculating and assessing the poor fit. Common errors include miscalculating expected like B, demanding exactness as in C, or assuming uniformity like D. Developing: (1) collect frequencies, (2) calculate relative frequencies, (3) assign probabilities, (4) verify sum=1; comparing: calculate expected, assess deviation. Non-uniform models account for patterns, and mistakes involve exact expectations or ignoring data discrepancies.

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