What is the prob of answering any 3 questions correctly?

[amy-lee]

I'm not sure if I answered this right.

1.The multiple choice section of a test consists of 5 questions. Each question has 4 choices and is answered by guessing.

a)What is the probability of answering any 3 questions correctly? Round your answer to the nearest one hundredth of a percent.
P(any 3 correct)=5C3(1/4)^3(3/4)^5-3
=(10)(0.015625)(0.5625)
=0.087890625*100
=8.79%

 

[galactus]

That's it. You got it nailed. Good work.

 

[pka]

Actually I disagree with your answer.
The wording of the question implies “at least three”: 3, 4 or 5.