A laptop company claims up to 8.1 hours of wireless web usage for its newest laptop battery life. However, reviews on this laptop shows many complaints about low battery life. A survey on battery life reported by customers shows that it follows a normal distribution with mean 7.5 hours and standard deviation 27 minutes. (a) What is the probability that the battery life is at least 8.1 hours

0.0918 = 9.18% probability that the battery life is at least 8.1 hours.

Step-by-step explanation:

Normal Probability Distribution:

Problems of normal distributions can be solved using the z-score formula.

In a set with mean and standard deviation , the z-score of a measure X is given by:

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 p-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.

Mean 7.5 hours

This means that

Standard deviation 27 minutes.

An hour has 60 minutes, which means that

What is the probability that the battery life is at least 8.1 hours?

This is 1 subtracted by the p-value of Z when X = 8.1. So

has a p-value of 0.9082.

1 - 0.9082 = 0.0918

0.0918 = 9.18% probability that the battery life is at least 8.1 hours.