Hairy ears are inherited as a Y-linked trait. A man with hairy ears has a daughter who has a son with a man who does not have hairy ears. What is the probability that the hairy-eared man's grandson has hairy ears?

zero

Explanation:

Y-linked traits do not occur in females as they do not possess the Y chromosome, and occur in all male descendants of an affected male. Since the affected grandfather produces daughter. She is unaffected and then mates with an unaffected male that does not have hairy hairs. The son produced between them will not have hairy hairs.

If the grandfather had sired a son, his son will be affected and then the son can pass on this trait to his own son.