Question

One card is selected at random from a deck of cards. Determine the probability that the card is a 3 or 7.

Answer 1

P ( A or B ) = P (A) + P (B) - P ( A and B )
P ( 3 or 7 ) = P (3) + P (7) - P ( 3 and 7 )
= 4/52 + 4/52 - 0 (a card can't be both)
= 1/13 + 1/13 = 2/13