math
posted by Melissa on .
A card is selected from a deck of 52 playing cards. Find the probability of selecting
· a prime number under 10 given the card is a heart. (1 is not prime.)
· a diamond or heart given the card is red.
· a King, given that the card is not a spade.
Show step by step work. Give all solutions exactly in reduced fraction form

conditional probability:
P(AB) read: prob of A, given B
= P(A∩B)/P(B)
let A be all primes under 10
B is all hearts
so A∩B is 2H, 2H, 5H, 7H, there are 4 of those
prob(prime under 10  red) = (4/52)/(1/4) = 4/13
Here is a page with a nice explanation and examples of conditional probability.
(Broken Link Removed)