Sat scores. sat scores of students at an ivy league college are distributed with a standard deviation of 250 points. two statistics students, raina and luke, want to estimate the average sat score of students at this college as part of a class project. they want their margin of error to be no more than 25 points. (a) raina wants to use a 90% confidence interval. how large a sample should she collect? (b) luke wants to use a 99% confidence interval. without calculating the actual sample size, determine whether his sample should be larger or smaller than raina's, and explain your reasoning. (c) calculate the minimum required sample size for luke.

The confidence interval for confidence level of is

where is the sample mean, is the critical value for the given confidence level, is the standard deviation of the population, and is the sample size. The margin of error is the term.

a) For a confidence level of , we have . So in order to have a margin of error of at most 25 points, we have

so Raina should collect a sample of at least 269 students.

b) A confidence interval with a higher confidence level would more closely approximate and reflect the population, so it stands to reason that Luke should collect a larger sample than Raina to meet his 99% confidence spec.

c) For a confidence level of , we have . Then the margin of error would at most satisfy

so that Luke should collect a sample of at least 666 students.

starting with:    

5 + x - 12 = 2x - 7   

5 + x - 12 - x = 2x - 7 - x (subtract x from both sides)   

5 - 12 = x - 7 (combine and cancel x's from both sides)   

5 - 12 + 7 = x - 7 + 7 (add 7 to both sides)   

0 = x (add numbers together on both sides)       

so in order for the equation to be true, x must be 0.   

trying x = -0.5   

5 + x - 12 = 2x - 7 (original equation)   

5 + -0.5 - 12 = 2(-0.5) - 7 (plug in value of x)   

5 + -0.5 - 12 = -1 - 7 (did multiplication)   

-7.5 = -8 (did addition on both sides)       

since -7.5 is obviously not equal to -8, the value of -0.5 for x is wrong.   

trying x = 0   

5 + x - 12 = 2x - 7 (original equation)   

5 + 0 - 12 = 2(0) - 7 (plug in value of x)   

5 + 0 - 12 = 0 - 7 (did multiplication)   

-7 = -7 (did addition on both sides)       

since -7 equals -7, that demonstrates that the value of 0 for x is correct.   

trying x = 1   

5 + x - 12 = 2x - 7 (original equation)   

5 + 1 - 12 = 2(1) - 7 (plug in value of x)   

5 + 1 - 12 = 2 - 7 (did multiplication)   

-6 = -5 (did addition on both sides)       

since -6 is obviously not equal to -5, the value of 1 for x is wrong.