Q-4(a) An electric firms manufactures light bulbs that have a length of life that is normally distributedwith mean equal to 6.4 hours and standard deviation 2.7 hours. Find the probability that a bulb burns between 4 and 5 hours.

[2.5 Marks]

Q-4(b) The average yearly Medicare Hospital Insurance benefit per person was $4064 in a recent year. If the benefits are normally distributed with a standard deviation of $460, find the probability that the mean benefit for a random sample

of 20 patients is More than $4100.[2.5 Marks]