Answer :
In probability problems, look out for the word OR and AND.
OR means adding the probability
AND means multiplying the probability
P(a) = P(jack) + P(queen) + P(king) = (4/52) + (4/52) + (4/52) = 12/52 = 3/13
P(b) = [P(9) + P(10) + P(jack)] × P(red) = [(4/52) + (4/52) + (4/52)] × (26/52)
P(b) = (12/52) × (26/52) = 3/26
P(c) = 13/52 = 1/4
P(d) = P(a diamond) + P(a heart) + P(a spade) = (13/52) + (13/52) + (13/52) = 3/4
OR means adding the probability
AND means multiplying the probability
P(a) = P(jack) + P(queen) + P(king) = (4/52) + (4/52) + (4/52) = 12/52 = 3/13
P(b) = [P(9) + P(10) + P(jack)] × P(red) = [(4/52) + (4/52) + (4/52)] × (26/52)
P(b) = (12/52) × (26/52) = 3/26
P(c) = 13/52 = 1/4
P(d) = P(a diamond) + P(a heart) + P(a spade) = (13/52) + (13/52) + (13/52) = 3/4