Tommy's Tick-Tock Troubles
RAY: When Tom leaves for the barbershop, he sets his clock, the clock that had been flashing. And let's say he sets it for noon. So, he just presses set and the thing starts keeping time from that point on. At which point, he walks to the barbershop.
When he gets to the barbershop, he notices what time it is. And he sits there and reads his Field & Stream magazine and True Romance, True Detective, gets his haircut and he leaves. He notices what time it is then.
So he knows how much time he spent at the barbershop either waiting or getting his haircut.
RAY: When he gets home, he knows how much time has elapsed since he left because he set the clock. Let's say, for example, he set the clock at noon. When he got back, it was three o'clock according to his clock in his office.
TOM: So I know that altogether I've been gone for three hours.
RAY: And you know how long you spent in the barbershop which was what? Two hours.
TOM: Two hours.
RAY: So if you were gone for three and spent two hours --
TOM: Spent half an hour to get there and half an hour to get back.
RAY: So if he knows that, for example, he left the barbershop at five, then he had to have arrived home at 5:30. He sets his clock as what? Time for his late afternoon nap!
[ Car Talk Puzzler ]