Ok so there are 52 cards in a deck if you take all the cards that have the number 6 which is only 4 cards so 52-4 = 48 cards without any 6 so the ratio is 48/52 chances.
If you're trying to take any card that is greater than 6 its a little more complex there is T,2,3,4,5,6,7,8,9,10,B,Q,K so you have to tack away 6,7,8,9,10,B,Q,K from 4 rows so 8 x 4 =32 cards 52-32= 20 so the probability of not having any cards greater than 6 is 20/52
