normal distribution and probability HELP?

Almondzqueen · #1 $Old$ November 3rd, 2009, 06:01 AM

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?

Robb · #2 $Old$ November 3rd, 2009, 06:16 AM

$Y dsn N(60000,1400)$

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..