NCERT Solutions
Class 12 Maths
Probability

Ex.13.4 Q.17
Suppose that two cards are drawn at random from a deck of cards. Let X be the number of aces obtained. Then the value of E(X) is
(A)
Let X denote the number of aces obtained. Therefore, X can take any of the values of 0, 1, or 2.
In a deck of 52 cards, 4 cards are aces. Therefore, there are 48 non-ace cards.
So, P(X = 0) = P(0 ace and 2 non-ace cards) = (4C0 × 48C2)/ 52C2
P(X = 1) = P(1 ace and 1 non-ace cards) = (4C2 × 48C0)/ 52C2
P(X = 2) = P(2 ace and 0 non- ace cards) = (4C2 × 48C0)/ 52C2
Thus, the probability distribution is as follows:
|
X |
0 |
1 |
2 |
|
P(X) |
|
|
|
Then, E(X) = Σ Xi × P(Xi)
Let X denote the number of aces obtained. Therefore, X can take any of the values of 0, 1, or 2.
In a deck of 52 cards, 4 cards are aces. Therefore, there are 48 non-ace cards.
So, P(X = 0) = P(0 ace and 2 non-ace cards) = (4C0 × 48C2)/ 52C2
P(X = 1) = P(1 ace and 1 non-ace cards) = (4C2 × 48C0)/ 52C2
P(X = 2) = P(2 ace and 0 non- ace cards) = (4C2 × 48C0)/ 52C2
Thus, the probability distribution is as follows:
|
X |
0 |
1 |
2 |
|
P(X) |
|
|
|
Then, E(X) = Σ Xi × P(Xi)
Therefore, the correct answer is option D.
Therefore, the correct answer is option D.