There are three scenarios.
Either two are kings, only one card is king, none of the two is king.
In all, the number of combinations of taking 2 cards out of 6
=6C2==15 Split of this is like this:
The number of combinations of the two cards being kings =
2C2=1The number of combinations of only one card being a king
=2C1×4C1=2×4=8The number of combinations of neither cards being a king
=4C2=6Now, a = P(at least one king) = P(one king) + P(two king)
=(8+1)=b = P(no king)
==⇒==1.5