Thursday

July 31, 2014

July 31, 2014

Posted by **Jean** on Sunday, April 13, 2008 at 1:26pm.

- statistics -
**MathGuru**, Tuesday, April 15, 2008 at 11:26pmUse z-scores.

z = (x - mean)/sd

With your data:

z = (78 - 68.2)/10.4 = 0.94

.1736 is the probability using a z-table for a single student with a score greater than 78.

Now we can use a normal approximation to the binomial distribution.

mean = np = (75)(.1736) = 13

standard deviation = √np(1-p) = √(75)(.1736)(.8264) = 3.28

Again, use z-scores.

z = (20 - 13)/3.28 = 2.13

Use the z-table to find the probability. (Remember the problem says "at least 20" which means 20 or more.)

I hope this will help.

**Related Questions**

statistics - A final exam in Math 157 is normally distributed and has a mean of ...

Statistics - 5. Scores on a recent national statistics exam were normally ...

statistic - solve the problem :score a test are normally distributed with a mean...

statistics - Suppose that SAT scores among U.S. college students are normally ...

business statistics - Your statistics instructor wants you to determine a ...

statistics - Scores on the ACT test are normally distributed with a mean of 21.1...

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

statistics - Scores on a visual perception test are normally distributed with a ...

Statistics - Scores on a visual perception test are normally distributed with a ...

statistics - In a psychology class of 100 students, test scores are normally ...