Note: You'll need the Normal Distribution Table.(adsbygoogle = window.adsbygoogle || []).push({});

A certain type of light bulb has a lifetime in hours which is normally distributed with mean μ=650 and standard deviation σ=40. What is the probablility that a randomly selected light bulb has a lifetime in the range (700, 850)?

Now this is how I tried to do this:

We have to find P(700 ≤ X ≤ 850), but we need it in terms of Z.

Now,

Z= (X-μ)/σ

Z= (X-650)/40

But we have to apply this to all the sides of the inequality, so we end up with

P(1.25 ≤ (X-650)/40 ≤ 5)

= P(1.25 ≤ Z ≤ 5)

But using the Normal Distribution Table, there is no probability for the "5" bit of the inequality. So I'm not sure how to do this.

Thanks.

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Statistics Help

**Physics Forums | Science Articles, Homework Help, Discussion**