Question

A scientist compares the weights of strawberries from two different groups. The difference between the means of the weights for the two different groups is –10 grams. The scientist uses simulations to create a randomization distribution to try to determine the likelihood that the results happened by chance. The histogram represents the results of the 1,000 trials from the simulations.

Histogram. differences in means from random grouping.

According to the randomization distribution, is the difference in means due to chance or the group from which the measurements were made? Explain your reasoning.

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A botanist is studying the research question, “Do seeds from a common plant take longer to germinate at 72 degrees Fahrenheit or at 75 degrees Fahrenheit?” They design an experiment in which they select 20 seeds and assign those seeds to 2 groups of 10 seeds each at random. The seeds in the first group are placed in an environment that is held at a constant temperature of 72 degrees Fahrenheit, and the seeds in the second group are placed in an environment that is held at a constant temperature of 75 degrees Fahrenheit. The germination times, in days, for each group are displayed in the table.

group 1 days to germinate group 2 days to germinate
14 14
14 13
14 14
13 14
13 13
14 13
15 14
14 14
14 15
15 13
The mean germination time for group 1 is 14 days, and the mean germination time for group 2 is 13.7 days.

a. How could the botanist get a randomization distribution to compare the two groups?

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b. How would the botanist use the randomization distribution to determine whether the difference between the mean germination time for group 1 and the mean germination time for group 2 is due to chance?

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Noah rolls a standard number cube 10 times and adds the values to get a sum of 28. Is that unusually low? Clare simulates rolling the number cube 10 times on a computer and adds the values. She repeats that process 100 times and creates a histogram of the results.

Histogram from 22 to 48 by 2’s. Sum of 10 rolls. Height of each bar is 1, 3, 4, 9, 9, 11, 16, 14, 12, 10, 5, 5, 1.

a. Based on the histogram, does 28 seem unusually low?

Select the correct choice.


A YesYes

B NoNo
Explain your reasoning.

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b. The mean of Clare’s simulations is a sum of 35, and the standard deviation is 5.72. Using a normal distribution as an approximation of this distribution, what is the probability that a person would roll a sum less than 28? Round your answer to the nearest hundredth.

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Answer 1

Answer: According to the histogram, a sum of 28 is not unusually low. The bar representing a sum of 28 has a height of 9, which is relatively high compared to some of the other bars. Additionally, the histogram is roughly symmetric, so a sum of 28 is not far from the mean of the distribution.

To find the probability that a person would roll a sum less than 28, we can standardize the value using the formula z = (x - mu) / sigma, where x is the sum of 28, mu is the mean of 35, and sigma is the standard deviation of 5.72.

z = (28 - 35) / 5.72 = -1.22

Using a standard normal distribution table or calculator, we can find that the probability of getting a z-score less than -1.22 is approximately 0.1112, or 11.12%. Therefore, there is about an 11.12% chance that a person would roll a sum less than 28.

Explanation: