normal distribution

Question

Laboratory tests show that the lives of light bulbs are normally distributed with a mean of 750 hours and a standard deviation of 75 hours. Find the probability that a randomly selected light bulb will last between 825 and 900 hours.

Answer 1

This is similar to the problems i solved overnight. The range 825-900 is 75-150 away from the mean. Since the standard deviation is 75, this is 1-2 std dev's away from the mean. The standard charts show 13.6% of the normal distribution is between 1-2 std dev's from the mean, in one direction. So 13.6% is the answer.