CBSE Class 12 Math 2008 Solved Paper

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Question : 22
Total: 29
A pair of dice is thrown 4 times. If getting a doublet is considered a success, find the probability distribution of the number of successes.
Solution:  
Total number of outcomes = 36
The possible doublets are (1, 1), (2, 2), (3, 3), (4, 4), (5, 5), and (6, 6).
Let p be the probability of success, therefore,
p =
6
36
=
1
6

So, q = 1 - p = 1 -
1
6
=
5
6

Since the dice is thrown 4 times, n=4
Let X denote the number of times of getting doublets in the experiment of throwing two dice simultaneously four times.
Therefore X can take the values 0, 1, 2, 3, or 4.
P (X = 0) =
4
‌
C0p0q4
= (
5
6
)
4
=
625
1296

P(X = 1) =
4
‌
C1p1q3
= 4 (
1
6
)
(
5
6
)
3
=
500
1296

P(X = 2) =
4
‌
C2p2q2
= 6 (
1
6
)
2
(
5
6
)
2
=
150
1296

P (X = 3) =
4
‌
C3p4q0
= (
1
6
)
4
=
1
1296

Thus, the probability distribution is:
X 0 1 2 3 4
P (X)
625
1296
500
1296
150
1296
20
1296
1
1296

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