Puzzle

I HAVE two taps, one of which can fill a cup in 20 seconds, the other in 10 seconds. They are too far apart to put a cup under both at the same time. How quickly can I fill three cups, and how do I do it?

Answer to yesterday's puzzle:

FISH-FIST-FIAT-FLAT-FLAP- CLAP-CHAP-CHIP.

(The answer to today's puzzle will appear tomorrow.)