From Josh of Alameda School, Ampthill, Beds:

There are 5 presents in the second pile, 2 presents in the first pile, 3 presents in the third pile and 10 in the fourth pile.

I worked it out by saying the second pile equalled x. The first pile would then be x-3, the third pile x-2 and the fourth pile was 2x.

Simplified this gave me 5x-5 = 20. So 5x = 20+5. 5x = 25. And so x, the number of presents in the second pile, is 5.