6.36 The inter-accident times (times between accidents)

for all fatal accidents on scheduled American domestic passenger air flights, 1948–1961, were found to follow an exponential distribution with a mean of approximately 44 days (Pyke, J. Royal Statistical Society

(B),27, 1968, p. 426).

a If one of those accidents occurred on July 1, find the probability that another one occurred in that same month.

b Find the variance of the inter accident times.

c What does the information given above suggest about the clumping of airline accidents?