Question

When Hailey commutes to work, the amount of time it takes her to arrive is normally distributed with a mean of 21 minutes and a standard deviation of 3.5 minutes. Out of the 211 days that Hailey commutes to work per year, how many times would her commute be between 19 and 26 minutes, to the nearest whole number?

Answer 1

Answer: 135 days

Step-by-step explanation:

Since the amount of time it takes her to arrive is normally distributed, then according to the central limit theorem,

z = (x - µ)/σ

Where

x = sample mean

µ = population mean

σ = standard deviation

From the information given,

µ = 21 minutes

σ = 3.5 minutes

the probability that her commute would be between 19 and 26 minutes is expressed as

P(19 ≤ x ≤ 26)

For (19 ≤ x),

z = (19 - 21)/3.5 = - 0.57

Looking at the normal distribution table, the probability corresponding to the z score is 0.28

For (x ≤ 26),

z = (26 - 21)/3.5 = 1.43

Looking at the normal distribution table, the probability corresponding to the z score is 0.92

Therefore,

P(19 ≤ x ≤ 26) = 0.92 - 28 = 0.64

The number of times that her commute would be between 19 and 26 minutes is

0.64 × 211 = 135 days