# normal distribution and probability HELP?

• Nov 3rd 2009, 05:01 AM
Almondzqueen
normal distribution and probability HELP?
The tread life of a particular brand of tire is a random variable best described by a normal distribution with a mean of 60,000 miles and a standard deviation of 1400 miles. What is the probability a particular tire of this brand will last longer that 58,600?

what formula do I particularly use here?
• Nov 3rd 2009, 05:16 AM
Robb
$Y dsn N(60000,1400)$

So you want
$P(Y>58000)$which can be converted to standard normal using
$\frac{y-\mu}{\sigma}=\frac{58000-60000}{1400}=-1.42857$

So
$P(Z>-1.42857)$
So you should be able to use a standard normal table to calculate this using symmetry..