Critical-part failures in NASCAR vehicles. In NASCAR races such as the Daytona 500, 43 drivers start the race;

however, about 10% of the cars do not finish due to the failure of critical parts. University of Portland professors conducted a study of critical-part failures from 36 NASCAR races (The Sport Journal, Winter 2007). The researchers discovered that the time (in hours) until the first critical-part failure is exponentially distributed with a mean of .10 hour.

a. Find the probability that the time until the first critical-part failure is 1 hour or more.

b. Find the probability that the time until the first critical-part failure is less than 30 minutes.