Posted by **Student** on Sunday, March 4, 2012 at 2:28pm.

Darby guesses the answers to six questions on the math portion of her college entrance exam. Each question is a true or false question. What is the approximate probability that at least 4 of her answers are correct?

A. 0.23

B. 0.34

C. 0.66

D. 0.78

Explanation please??

- Probability -
**MathMate**, Sunday, March 4, 2012 at 4:22pm
The answer is

(n,r)/2^n

Here there are 6 questions, so n=6, and

there are 2^6=64 possible sets of answers.

Since 4 of them are right, the number of combinations with 4 correct out of 6 is

(n,r)=(6,4)=6*5/(1*2)=15

What would be the probability that 4 out of six are correct if the answers are completely random?

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