Posted by **Amy** on Saturday, July 11, 2009 at 2:30pm.

A quiz consists of 10 multiple-choice questions, each with 4 possible answers. For someone who makes random guesses for all of the answers, find the probability of passing if the minimum passing grade is 70 %.

I'm not sure what to do. I figured that there's 10 questions, each with a 1/4 chance. I took 10*1/4=2.5 and multiplied that by .70, but my answer wasn't right. What am I missing?

- Probability/Statistics -
**Reiny**, Saturday, July 11, 2009 at 2:53pm
To pass he must guess

1. exactly 7 out 10 or

2. exactly 8 out 10 or

3. exactly 9out 10 or

4. exactly 10 out 10

prob of exactly 7 out 10 = C(10,7)(1/4)^7(3/4)3 = 120(1/16384)(27/64) = .00309

prob of exactly 8 out 10 = C(10,8)(1/4)^8(3/4)^2 = .000386

prob of exactly 9 out 10 = C(10,9)(1/4)^9(3/4) = .000018

prob of exactly 10 out 10 = C(10,10)(1/4)^10 = .00000095

for a total of .0035055 as the probability.

suggestion: study, and don't guess

## Answer This Question

## Related Questions

- Finite Math - A quiz consists of 10 multiple-choice questions, each with 5 ...
- Statistic - A quiz consists of 10 multiple-choice questions. Each question has 5...
- Finite Math - A biology quiz consists of 10 multiple -choice questions. 7 must ...
- Binomial Distribution - A biology quiz consists of twelve multiple-choice ...
- Probability - What is the probability of passing a 10-item multiple choice quiz...
- Statistics - A multiple choice test consists of 60 questions. Each question has ...
- math - I have no idea where to start! *A quick quiz consists of 3 multiple ...
- statistic - A statistics quiz consists of 10 multiple questions. There are four ...
- stat probability - A multiple choice quiz consists of 20 questions, each with 3 ...
- statistics - A multiple-choice test consists of 29 questions with possible ...

More Related Questions