A card is drawn at random from a well-shuffled deck of playing cards. Find the probability that the card drawn is (i) a card of spades or an ace, (ii) a red king, (iii) either a king a queen, (iv) neither a king nor a queen.
Total numbers of elementary events are: 52
(i) Let E be the event of drawing a card of spade or an ace
Let A be the event of drawing a card of spade
The favourable numbers of drawing a card of spade are: 13
P (spade) = P (E) = 13/52
Let B be the event of drawing an ace
The numbers of favourable outcomes are: 3 one ace being spade card already been counted
P (ace) = P (B) = 3/52
∴ P (spade or ace) = P (E) = P (A) + P(B) = 13/52 + 3/52 = 16/52 = 8/26 =4/13
(ii) Let E be the event of drawing a red king
The numbers of favourable outcomes are: 2
∴ P (red king) = P (E) = 2/52 = 1/26
(iii) Let E be the event of drawing either a king or a queen
Let A be the event of drawing a king
Then, the numbers of favourable outcome are: 4
P (king) = P (A) = 4/52
Let B be the event of drawing a queen
Then, the numbers of favourable outcome are: 4
P (queen) = P (B) = 4/52
∴ P (king or queen) = 4/52 + 4/52 = 8/52 = 2/13 -----@
(iv) Let E be the event of drawing neither a king nor a queen
P (getting either king or a queen) = 2/13 (part c above ----@)
∴ P (neither king nor queen) = P (E) = 1 – P (either king or queen) = 1 – 2/13 = 11/13