posted by Harikays .
A set of 15 cards numbered 1 to 15. One card is drawn at random. What is the probability that it is a multiple of 3 of 5 or both?
There are 15 cards in total. Cards that are numbered with multiples of 3 are: 3, 6, 9, 12, 15. Cards that are numbered with multiples of 5 are: 5, 10, 15. 15 is a multiple of both numbers so it only needs to be counted once and if we count the other cards that is a total of 7 cards out of the 15. This makes the probability 7 out of 15 or 7/15.