Logic challenge

There are 3 light bulbs in the attic, and three light switches in the basement. You need to figure out which light switch controls which light bulb (One switch controls one bulb). How can you determine which switch controls which bulb, by starting in the basement, and making only 1 trip to the attic. You can not see any light or the light bulbs unless in the attic.

Math challenge

Using only three 9's and the usual math symbols (+ _ x / . exp square root (), etc, can you equal 20? No tricks!