In a standard deck of cards, how many different sets of 4-of-a-kind are there?

There are 13 different 4 of a kinds.
4 aces 4 twos 4 threes 4 fours 4 fives 4 sixes 4 sevens 4 eights 4 nines 4 tens
    1           2         3           4          5         6             7            8           9          10 
4 jacks 4 queens 4 kings
    11         12          13
The answer is 13 different sets.
I hope this helps :)

20 percentage, you can also do it on a calculator.