# Thread: Normal Distribution using probability

1. ## Normal Distribution using probability

A question says that "The distribution of lifetimes for a certain type of light bulb is normally distributed with mean 1000hours and standard deviation of 100hours. What is the 33rd percentile of the distribution of lifetimes?" How will I do it?

2. ## Re: Normal Distribution using probability

You will need to look up on an inverse normal table what value of z gives an area of 0.33 and then get the x value from the formula \displaystyle \begin{align*} z = \frac{x - \mu}{\sigma} \end{align*}.