1 Use the cumulative distribution function for the standard

1) Use the cumulative distribution function for the standard normal (z) to find the probability of a value between 7 and 13 drawn from a normal distribution with mean 10 and variance 4.

2) The lifetime of a light bulb is an exponential random variable with a mean of 1000 hours.The light bulb is guaranteed to last at least 900 hours.

a) Find the probability density function for this random variable.