AP Statistics Inference for the Difference of Two Means Quiz: 10 Questions with Explanations

A 1.08B 0.89C 2.28D 9

sqrt(16/30 + 25/40) = sqrt(0.5333 + 0.625) = 1.076. Adding the standard deviations or the variances without dividing by n are common errors.

A A two-sample t procedureB A paired t procedureC A two-proportion z procedureD A chi-square test

The same students are measured twice, so we analyze the differences.

A 0.026B 0.5C 0.987D 0.013

With df = 20, P(t > 2.4) is about 0.013.

A the groups must be equal in sizeB the means are equalC the sample proportions are at least 10D each group is approximately normal or has n at least 30

Each group must satisfy the condition; equal sizes are not required.

A mu1 is larger than mu2B mu2 is larger than mu1C the means are equalD the samples were paired

The whole interval is positive, so 0 is not plausible and mu1 is larger.

A a pooled proportionB only the larger standard deviationC each group’s own standard deviation and sample sizeD the sum of the standard deviations

SE = sqrt(s1^2/n1 + s2^2/n2).

A The 10% conditionB Random assignment to the groupsC Equal sample sizesD A paired design

Random assignment provides the independence needed for the comparison.

A A higher confidence levelB Larger standard deviationsC Larger samplesD Smaller sample sizes

A larger n reduces the standard error.

A 0.69B 0.35C 0.04D 0.96

The tail area beyond 0.4 is about 0.345; doubling gives 0.69.

A paired tB two-sample tC chi-squareD one-proportion z

Different plants receive each treatment, so the groups are independent.