Calculating SAT Score Probability: Sample Mean vs Population Mean

[yeungmei]

Please please help me, i totally forgot about Stat and now i have a question due tomm.

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?

Please please help !

 

[vsage]

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

 

[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?

 

[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

 

[yeungmei]

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

 

[vsage]

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

 

[yeungmei]

Got it..Thanks ^__^