Exactly 1/4 of a 52-card deck of cards is clubs. Another 1/4 spades, another 1/4 is hearts, and the final 1/4 is diamonds. To find what one fourth of 52is, you can divide 52 by 4. That equals 13. So there are 13 clubs in the entire deck of cards. If you are trying <em>not </em>to get a club, you have to find the remainder of the cards without those 13. 52 - 13 = 39. This means that you have 39/52 odds of <em>not </em>getting a club. Simplified you get 3/4.
I did it the long way. A shorter was is to see that, obviously, one whole minus one fourth is three fourths.