flashcards question

[mmk88]

this is from the MGMAT Flash Cards WT 10.

Q: Is the statement sufficient?

Eight participants in a psychology exp are given different amounts of money at the beginning of the experiment. Will the average amount of money each participant has at the end of the experiment be higher than, lower than, or equal to the avg that each participant had at the beginning of the expt?

1)Half of the participants are asked to give 20% of the original money back, while the other half are given an additional 25%


The answer is Insufficient ? Dosent make sense to me based on the following logic



4 people ... 100 dollars each .. avg 100

2 people 25% more, 2 people 20% less ... 80,80, 125, 125 = avg = 410/ 4 which is more than 100 .... should be sufficient ?

[tim]

you can't pick one set of sample numbers (that doesn't work according to the rules of the problem), get an answer, and conclude that the statement is sufficient. pick another couple of samples and see what happens. make sure you follow the constraints of the problem this time though..

[andy.wy.tam]

Eight participants in a psychology experiment are given different amounts of money at the beginning of the experiment. Will the average amount of money each participant has at the end of the experiment be higher than, lower than, or equal to the average that each participant had at the beginning of the experiment?

(1) Half of the participants are asked to give 20% of the original money back, while the other half are given an additional 25%.

I am confused with the verbiage...

If we're asked to find the average amount of money EACH participant has at the end of the experiment, won't we know?

i.e., we have 8 people, half with 20% taken away, half given 25%... but the average amount EACH participant has at the end is simply what they had before less 20% of what they had, or 25% more of what they had before...

If the question was asking what the average amount of money the group of participants have then I understand... however it's this EACH participant thing that is hanging me up. Can any GMAT instructors please clarify?

Thanks.
Andy

[tim]

The question is asking whether we know what happens to the average with just the information given at the top - that they are all given different amounts. Without knowing more about the amounts each participant has, we cannot answer this. If we knew specific numbers, then yes we could calculate what happened to the average. But we don't have this information.