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1 Answer

Probability of solving one problem=85/100=0.85. Let p=0.85. The probability of failing to solve a problem is 1-p=0.15. Let q=0.15, then (p+q)4=1 represents all possible outcomes.

(p+q)4=p4+4p3q+6p2q2+4pq3+q4=1.

In words, these terms represent:

all questions correct

3 correct, 1 wrong

2 correct, 2 wrong

1 correct, 3 wrong

all wrong

So exactly three correct is the second term 4p3q=4(0.85)3(0.15)=0.368 or 36.8% approx.

by Top Rated User (894k points)

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