Sean and Evan are college roommates who have part-time jobs as servers in restaurants.

Jadiel Bowers

Jadiel Bowers

Answered question

2023-02-20

Sean and Evan are college roommates who have part-time jobs as servers in restaurants. The distribution of Sean’s weekly income is approximately normal with mean $225 and standard deviation $25. The distribution of Evan’s weekly income is approximately normal with mean $240 and standard deviation $15. Assuming their weekly incomes are independent of each other, which of the following is closest to the probability that Sean will have a greater income than Evan in a randomly selected week?
1) 0.67
2) 0.7000
3) 0.227
4) 0.303
5) 0.354

Answer & Explanation

alihikaua8xxc

alihikaua8xxc

Beginner2023-02-21Added 9 answers

The correct answer is 4 0.303
Explanation for the correct answer:
Step 1: Problems of normal distributions can be solved using the z-score formula:
In a set with mean μ and standard deviation σ , the z-score of a measure X is given by:
Z = X μ σ
The Z-score measures how many standard deviations the measure is from the mean.
After finding the Z-score, we look at the z-score table and find the z-value associated with this z-score.
This p-value is the probability that the value of the measure is smaller than X, that is, the percentile of X. Subtracting 1 by the p-value, we get the probability that the value of the measure is greater than X.
Subtraction between normal variables:
When two normal variables are subtracted, the mean is the mean difference, and the standard deviation is the square root of the sum of the variances.
In this question:
We want the probability that Sean has a higher income than Evan, which is the probability that dividing Sean's income by Evan's income is greater than zero.
Step 2: Distribution of the difference between Sean's and Evan's income:
Sean has mean 225, Evan 240. So
μ = 225 240 = 15
Sean's standard deviation is of 25, Evan's of 15. So
σ = 25 2 + 15 2 = 625 + 225 = 850 = 29.15
Step 3: Probability that Sean will have a greater income than Evan in a randomly selected week:
Probability of the subtraction being greater than 0, which is 1 subtracted by the p value of Z when X = 0 .
So
Z = X μ σ Z = 0 ( 15 ) 29.15 Z = 15 29.15 Z = 0.51 Z = 0.51 has a p-value of   0.695 1 0.695 = 0.305 0.303
Thus, the correct answer is option D

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