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14.Probability
normal
Three randomly chosen nonnegative integers $x, y$ and $z$ are found to satisfy the equation $x+y+z=10$. Then the probability that $z$ is even, is
A
$\frac{36}{55}$
B
$\frac{6}{11}$
C
$\frac{1}{2}$
D
$\frac{5}{11}$
(IIT-2017)
Solution
Total number of solutions $={ }^{10+3-1} \mathrm{C}_{3-1}=66$
Favourable number of solutions $={ }^{11} \mathrm{C}_1+{ }^9 \mathrm{C}_1+{ }^7 \mathrm{C}_1+{ }^5 \mathrm{C}_1+{ }^3 \mathrm{C}_1+{ }^1 \mathrm{C}_1=36$
$\mathrm{P}(\mathrm{req})=\frac{36}{66}=\frac{6}{11}$
Standard 11
Mathematics