Math Problem Statement

Suppose Abby tracks her travel time to work for 60 days and determines that her mean travel time, in minutes, is 35.6. Assume the travel times are normally distributed with a standard deviation of 10.3 min. Determine the travel time x such that 29.46% of the 60 days have a travel time that is greater than x.

Solution

The problem presented asks us to determine a travel time, xx, such that 29.46% of the travel times exceed this value, given that Abby's travel times are normally distributed with a mean of 35.6 minutes and a standard deviation of 10.3 minutes.

This is a standard normal distribution problem. We need to find the value of xx for which 29.46% of the distribution is greater than xx. In terms of a z-score, this means we're looking for the z-value where the upper tail of the standard normal distribution is 29.46%.

Steps:

  1. Convert the percentage to a probability:
    29.46% translates to a probability of 0.2946. This is the area to the right of xx, so we are looking for a z-score where the area to the right is 0.2946, or equivalently, the area to the left is 10.2946=0.70541 - 0.2946 = 0.7054.

  2. Find the z-score corresponding to the cumulative probability of 0.7054 using standard normal tables or a calculator.

  3. Use the z-score formula:
    z=xμσz = \frac{x - \mu}{\sigma} where μ=35.6\mu = 35.6 (mean) and σ=10.3\sigma = 10.3 (standard deviation). Solve for xx once the z-score is known.

Let me calculate the z-score and the corresponding xx.

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Math Problem Analysis

Mathematical Concepts

Normal Distribution
Probability
Z-score

Formulas

z = (x - μ) / σ

Theorems

Empirical Rule
Properties of Normal Distribution

Suitable Grade Level

College-level Statistics