5.8 At the beginning of winter, a homeowner estimates that the probability is 0.4 that his total heating bill for the three winter months will be less than $380. He also estimates that the probability is 0.6 that the total bill will be less than $460.

a. What is the probability that the total bill will be between $380 and $460?

b. Given no further information, what can be said about the probability that the total bill will be less than $400?