An Air Force study indicates that the probability of a disaster such as the January 28, 1986 explosion of the space shuttle Challenger was 1 in 35....

.    An Air Force study indicates that the probability of a disaster such as the January 28, 1986 explosion of the space shuttle Challenger was 1 in 35. The Challenger flight was the 25th mission.

a.  How many disasters would you expect in the first 25 flights?

b.  Use the normal approximation to estimate the probability of at least one disaster in 25 missions.