RAY: Now, logic would tell you, well, if you bought two, it would then be June 15, right? But the answer is, instead of his lawn being finished on June 30, it's done on June 29, because all it does is gain him one day. Because don't forget, when you plant one, the next day, how many do you have? Two, right?
TOM: Well, you don't really have two.
RAY: You have double the size.
TOM: Double the size.
RAY: Which is what you get if you bought two of them. And what happens the next day? You've got four. So, all it does it lop off the first day. So that's the answer: he sprays it on June 29, and if it doesn't, then it eats his house.
[ Car Talk Puzzler ]