# Maths question - standard distribution

• Sep 27th 2008, 09:22 AM
Pikachu
Maths question - standard distribution
The working lie of 60 watt bulbs produced by Max Bulb CVo is normally distributed with a mean of 24.00 hours and a standard deviation of 6.06 hours.

what is the probability that a bulb at random is picked from this populatiohn with a working life of more than 29.11 hours?

Thanks
• Sep 27th 2008, 02:52 PM
mr fantastic
Quote:

Originally Posted by Pikachu
The working lie of 60 watt bulbs produced by Max Bulb CVo is normally distributed with a mean of 24.00 hours and a standard deviation of 6.06 hours.

what is the probability that a bulb at random is picked from this populatiohn with a working life of more than 29.11 hours?

Thanks

Obviously you have to calculate Pr(X > 29.11).

If you provide details on how you've been taught to calculate probabilities such as these (tables, technology, ....?) further specific help can be given.
• Sep 28th 2008, 10:10 PM
pickslides
I agree, find p(X>29.11)

The question refers to normal distribution so turn into a Z value

p(Z>(29.11-24)/6.06)

p(Z>0.95) = 0.17