Problem from Kaplan CAT 1: Is the answer C or E?

[pseudonym]

Hi All,

Encountered the following DS problem in Kaplan CAT 1. Have put my own reasoning and answer choice below. Point is I got it wrong; the software says the answer is C. Forum members and esp. Kaplan professors, need ur help pls!


At a certain dept store present-wrapping counter, each clerk will wrap no fewer than 20 and no more than 30 presents per hour. If 70 people are standing in line, will all of their presents be wrapped after one hour?

1) Each person in line has at least one present to be wrapped by one of the 6 clerks at the counter.
2) If each person in line had one more present to be wrapped, 9 clerks would be required to guarantee that every present would be wrapped in one hour.

It was obvious why the answer isn't A or D; statement 1 keeps the total no of presents very open ended - there could be 70 or 7000 presents here.

Here's my analysis of statement 2. The moment you require 9 clerks, it means the no of presents exceeds the max capacity of 8 clerks, i.e. 240. So if we consider each of the 70 guests having an extra present, total no of presents would range from 241 till 270 inclusive. Subtract 70, you get 171 till 200 inclusive (actual no of presents). If it's 180 or less, no of clerks needed is 6. If it's 181 till 200, 7 will suffice. Hence statement 2 doesn't suffice alone.

C is also incorrect: statement 1 tells us there are 6 clerks, statement 2 tells us the total no of presents would require 6 clerks or 7.

Hence the only remaining answer is E.

That was my solution. The Kaplan solution says the answer is C (both together suffice). It assumes that in statement 2, when each person in line has an additional present, total no of presents becomes 180 (9x20). From there it goes on to say that both statements together give us no of presents and clerks, so answer choice C is correct.

Once again, Kaplan tutors or GMAT titans out there, can u pls shed some light on this?

Thx, H

[Ian Stewart]

Here's my analysis of statement 2. The moment you require 9 clerks, it means the no of presents exceeds the max capacity of 8 clerks, i.e. 240. So if we consider each of the 70 guests having an extra present, total no of presents would range from 241 till 270 inclusive. Subtract 70, you get 171 till 200 inclusive (actual no of presents). If it's 180 or less, no of clerks needed is 6. If it's 181 till 200, 7 will suffice. Hence statement 2 doesn't suffice alone.

I don't like this question, because I think it's open to misinterpretation, but when they say '9 clerks would be required', they mean something like: 'to be 100% certain the presents would get wrapped, you would need to be sure to have at least 9 clerks'. So what they mean is 'even if you assigned the slowest imaginable clerks to the counter, if you had 9 of them, the presents will get wrapped'. So we're interested in the slowest clerks, which is why they use the rate of 20 presents per hour. Otherwise I think your approach is perfect. You won't see wording like that on the real test, so I wouldn't worry about this question much.