7.20 Let x denote the lifetime (in thousands of hours) of a certain type of fan used in diesel engines. The density curve of x is as pictured:

0 25 50 Shade the area under the curve corresponding to each of the following probabilities (draw a new curve for each part). (Hint: See Example 7.8.)

a. Ps10 , x , 25d

b. Ps10 # x # 25d

c. Psx , 30d

d. The probability that the lifetime is at least 25,000 hours

e. The probability that the lifetime exceeds 25,000 hours