For a certain type of computer, the length of time between charges of the battery is normally distributed with a mean of 50 hours and a standard deviation of 5 hours. Assuming there were 900 computers...

For a certain type of computer, the length of time between charges of the battery is normally distributed with a mean of 50 hours and a standard deviation of 5 hours. Assuming there were 900 computers that were put to test, how many computers have a battery life of between 40 to 60? (Answer is an integer)