It is estimated that 75% of a grapefruit crop is good; the other 25%have rotten centers that cannot be detected until the grapefruit are cut open. The grapefruit are sold in packs of 10. Let r be the number of good grapefruits in the sack.
(a) What is the probability of getting no more than one bad grapefruit in a sack? What is the probability of getting at least one good grapefruit in a sack?
(b) What is the expected number of good grapefruit in a sack?
(c) What is the standard deviation of the r-probability distribution?