In an agricultural experiment, a large field of wheat was divided into many plots (each plot being 7 x 100 ft) and the yield of grain was measured for each plot. These plot yields followed approximately a normal distribution with mean 88 lb and SD 7 lb.
a) Find the probability that any one randomly selected plot yield is greater than 90 lb.
b) For the five plots chosen at random, find the probability that at least 2 yield is greater than 90 lb.
c) Let Y represent the mean yield rate of five plots chosen at random from the field, find Pr(Y >90).