In an agricultural experiment, a large uniform field was planted with a single variety of wheat. The field was divided into many plots (each plot being 7 × 100 ft) and the yield (lb) of grain was measured for each plot. These plot yields followed approximately a normal distribution with mean 88 lb and standard deviation 7 lb. What percentage of the plot yields were
(a) 80 lb or more?
(b) 90 lb or more?
(c) 75 lb or less?
(d) Between 75 and 90 lb?
(e) Between 90 and 100 lb?
(f) Between 75 and 80 lb?