# Probability at steak! Plz Help

1. Sep 17, 2006

### yeungmei

The College Board American College Testing Progam reproted a population mean SAT score of U=1020. Assume that the population standard deviation is O-100

a) what is the probability that a random sample of 75 students will provide a sample mean SAT score within 10 of the population mean?

b) what is the probability a random sample of 75 students will provide a sample mean SAT score within 20 of the population mean?

2. Sep 17, 2006

### vsage

Do you know how to extract information from a z (normal distribution) chart?

3. Sep 17, 2006

### yeungmei

I know u-1020 is the average also the centre point of a curve, where i should get o-100 devidied by square root of 75 to find the standard deviation.

so for a, should i uses 10 / the calculated SD to find the probability???

4. Sep 17, 2006

### vsage

within 10 implies 10 points above or below the mean, so you would need to double any amount you found for the probability of finding the sample mean within 10 of the population mean from one side

Last edited by a moderator: Sep 17, 2006
5. Sep 17, 2006

### yeungmei

I thought it said within, so is it just use 10/SD to find???

6. Sep 17, 2006

### vsage

10/SD isn't within, that's one direction (up OR down, not both)

7. Sep 17, 2006

### yeungmei

Got it..Thanks ^__^