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CBSE Class 12 Math 2008 Solved Paper

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Question : 22 of 29
Marks: +1, -0
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 = 636\frac{6}{36} = 16\frac{1}{6}
So, q = 1 - p = 1 - 16\frac{1}{6} = 56\frac{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) =  4C0p0q4\,{}^{4}C_0 p^0 q^4 = (56)4\left(\frac{5}{6}\right)^4 = 6251296\frac{625}{1296}
P(X = 1) =  4C1p1q3\,{}^{4}C_1 p^1 q^3 = 4 (16)(56)3\left(\frac{1}{6}\right)\left(\frac{5}{6}\right)^3 = 5001296\frac{500}{1296}
P(X = 2) =  4C2p2q2\,{}^{4}C_2 p^2 q^2 = 6 (16)2(56)2\left(\frac{1}{6}\right)^2 \left(\frac{5}{6}\right)^2 = 1501296\frac{150}{1296}
P (X = 3) = 4C3p4q0{}^{4}C_3 p^4 q^0 = (16)4\left(\frac{1}{6}\right)^4 = 11296\frac{1}{1296}
Thus, the probability distribution is:
X 0 1 2 3 4
P (X) 6251296\frac{625}{1296} 5001296\frac{500}{1296} 1501296\frac{150}{1296}201296\frac{20}{1296} 11296\frac{1}{1296}
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