KVPY SX SB Exam 05-Nov-2017 Question Paper

Question : 9 of 120

Marks: +1, -0

A shooter can hit a given target with probability

1/4

. She keeps firing a bullet at the target until she hits it successfully three times and then she stops firing. The probability that she fires exactly six bullets lies in the interval

(0.5272, 0.5274)
(0.2636, 0.2638)
(0.1317, 0.1319)
(0.0658, 0.0660)

Validate

Solution:

^{\rd}

time target will hit in sixth time
So, In first 5 attempt these will be 3L, 2W and at 6

^{\th}

attempt shot will be hit
So,

^5C_3(3/4)^3×(1/4)^2×(1/4)

=270/4096= 0.06591

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