From a well shuffled pack of 52 playing cards two cards drawn at random. The probability that either both are red or both are kings is:
Assuming, cards are drawn without replacement:
Total possible events =52C2
P(both red) =26C252C2
P(both king) =4C252C2
P(both red & king) =2C252C2
We use the basic addition rule,
P(both black or both queens) = P(both red) + P(both queens) - P(both black as well as queens)
Required probability =26C2+4C2−2C252C2