PT155 S4 Q21 ExplanationAll of the students at Harrison

Answer choices, explained

1. A

   Correct45% picked this

   More than 38 percent of the students at Harrison who live in Pulham take

   Why this is right

   Pretend there are 100 students who live in W and 100 who live in Pulham. 200 total students go to this school. 29% of W takes a night class = 29 out of 100 38% of students overall do = 76 out of 100 So that would mean the other 47 ( = 76 - 29) students who take a night class come from Pulham. 47% of Pulham take a night class. That's how the math looks with equal sized Pulham and Westerville dorms. Since W is 9% below the overall average, Pulham would be 9% above the overall average in order to make the average be what it is. If Pulham and Westerville aren't equal sized, then Pulham's gap above 38% doesn't have to equal Westerville's gap below 38%, but it does still have to be the case that Pulham is above 38%. The school's overall rate of students taking night classes will always be a weighted average of the rate of Westerville students taking a night class and that of Pulham students taking a night class.

   Skill tested: Must be True · how this choice captures the argument's function is the move to repeat next time.

   45%
2. B

   Too Strong: more than 50%26% picked this

   More than 50 percent of the students who take night classes at Harrison

   This is possible but not mandatory. If there were a lot more students in Westerville than in Pulham, then Pulham could easily have a higher than 50% rate of night students, but without that information there's no reason to think Pulham is above 50%. Pulham has to be higher than 38% for the overall average to settle at 38%, but we can't derive how much farther above 38% Pulham would be without knowing the ratio of students living in Pulham vs. Westerville.

   26%
3. C

   Out of Scope Comparison: # vs. %11% picked this

   More students at Harrison live in Westerville than live

   This discussion only involves relative ideas. We can't derive any real number comparison. However, if we knew the night school rates were like this ... Westerville = 29% overall = 38% Pulham = 55% ... that would prove that there are more students in W than in Pulham (because the overall average is closer to Westerville 's average than it is to Pulham's average). If you combine 5% alcohol beer and 45% alcohol whiskey and get a drink that is 7% alcohol, then you know that it's mostly beer, with a few drops of whiskey in there. If the combo was 42% alcohol, you would know that it's mostly whiskey, with a few drops of beer in there.

   11%
4. D

   Out of Scope15% picked this

   Harrison students living in Pulham are less likely than those living in Westerville to take more

   Out of Scope: more than one night class We couldn't possibly derive whether they take only one or more than one night class, since the data is only expressed in terms of whether or not you take at least one night class.

   15%
5. E

   Out of Scope Comparison4% picked this

   Night classes at Harrison have larger enrollments, on average, than day

   Out of Scope Comparison: Night classes vs. Day classes Enrollment We don't have any information about students per class for night or for day, so we can't possibly make this comparison about how dense, on average, night vs. day classes are.

   4%