Friday

January 30, 2015

January 30, 2015

Posted by **holly** on Thursday, July 5, 2007 at 5:17pm.

Let N be the number of questions. You are asking for the probability of getting N/5 or fewer wrong by randomly guessing.

Assume N>> 1 and use an error-function approximation for the number of questions answered correctly. The mean will be N/2 and the standard deviation will be sqrt[N*p*(1-p)] = (1/2)sqrtN, since p = 1/2 is the probability of getting each one right.

Inegrate the probability of correct answers from 0.8 N to N, which you can treat as infinity when N is very large.

The larger the value of N, the less likely you will be to get 80% right.

For N=25, I get a standard deviation of 2.5 about a mean of 12.5, and the probability of getting 20 or more right will be 0.0013. It becomes a much lower probability of N = 100. You need to use an error function table for this sort of problem.

**Answer this Question**

**Related Questions**

stats again - ok I get it, so once I get the prob figred for one person, how do ...

stats - A study by Hewitt Associates showed that 79% of companies offer ...

Stats - Find the P-value for a left tailed hypothesis test with a test statistic...

Stats - A group of 56 randomly selected students have a mean score of 30.8 and a...

stats - Test scores on a university admissions test are normally distributed, ...

Statistics PLEASE HELP FINAL IN 1 HOUR - Is a new hair shampoo product actually ...

Algerba 1 - I have to put these intergers in order from least to greatest. 12, -...

Probablity - Samir had prepared the problem tests for Stages 1 to 5 of Geometry ...

math - A random sample of 2000 adults showed that 1120 of them have stopped at ...

stats - To test the hypothesis H0 : ì = 100 against H1 : ì > 100, a ...