Hi!
P(A|B) means the probability A will happen given B has happened. P(AnB) is the probability both will happen, and P(B) is the probability B will happen.
You can figure out a formula from that, but here's the generally accepted one:
P(A|B) = P(AnB) / P(B)
P(AnB) = 5/7
P(B) = 7/8
Substitute values in:
P(A|B) = 5/7 / 7/8
P(A|B) = 5/7 * 8/7
P(A|B) = 40/49
