stats-percentage question

kitchen appliances don't last forever. The lifespan of all microwave ovens sold in the united states is approximately normally distributed with a mean of 9 years and a standard deviation of 2.5 years. what percentage of the ovens last more than 10 years?

a. 11.5%

b. 34.5%

c. 65.5%

d. 69%

e. 84.5%

Re: stats-percentage question

Standardise the data and find the value using the normal distribution table.

$\displaystyle \displaystyle P(X>X_0) = P\left( Z> \frac{X_0-\mu}{\sigma}\right) $

In your case

$\displaystyle \displaystyle P(X>10) = P\left( Z> \frac{10-9}{2.5}\right) = \cdots$