Interesting DS Question on rates and percentages

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Over the last two years, who made more money investing in the stock market, Leslie or Kerri?
(1) Leslie made an average (arithmetic mean) return of 20%, and Kerri made an average (arithmetic mean) return of 5%.
(2) Kerri started with two times as much money as Leslie.

A. Statement (1) BY ITSELF is sufficient to answer the question, but statement (2) by itself is not.
B. Statement (2) BY ITSELF is sufficient to answer the question, but statement (1) by itself is not.
C. Statements (1) and (2) TAKEN TOGETHER are sufficient to answer the question, even though NEITHER statement BY ITSELF is sufficient.
D. Either statement BY ITSELF is sufficient to answer the question.
E. Statements (1) and (2) TAKEN TOGETHER are NOT sufficient to answer the question, meaning that further information would be needed to answer the question.

(E) Though we know Leslie and Kerri's average returns, we have little idea as to what their total returns are.

These abstract questions are best solved with Plug In. This one can be solved by plugging in 1. For example, if Leslie made a 100% return one year and a -60% return the next year, the average return would be (100% – 60%)/2 = 20%.

However, Leslie would only be left with year one 100% and -60% = (1 + 1) (1 – 0.6) = 2(0.4) = 80% of her original investment. This means that she lost 20%!

So statement (1) is insufficient.

Furthermore, statement (2) is clearly insufficient by itself because no returns are given.
Combined with statement (1), statement (2) doesn’t make the distribution of returns any clearer, so the answer is (E).


My feedback to the author:

This question is not correct from GMAT point of view since in the given answer the author is assuming that the returns from the first year will be reinvested. Question does not clearly state that the returns from each year are reinvested the next year.

If one assumes that he gains are not invested again then final gain would be +20% instead of -20% for Leslie and in that case the answer would change to C.


Experts here please comment if my thinking is correct or am I totally screwed.
Source: — Data Sufficiency |

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by torontogmat.com » Thu Mar 13, 2008 7:12 am
It is GMAC that is screwed, not you. Their questions are littered with ambiguities. You just have to do your best to make an assumption about what they probably meant. I wish I could be more helpful.

In this case, the reinvestment issue goes away since either investor could lose 99.99% in the first year, and make whatever is required for the arithmetic mean *of their year 1 and year 2 returns* in the second year. This would allow either person to have essentially zero, so either could make more money.

The average 'of their year 1 and year 2 rates of return' would have been a better way to phrase this, since investors and business students would generally consider the 'average return' to be the net return divided by the number of years (neglecting adjustment for compound annual growth rate)

Shame on GMAC.

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by camitava » Thu Mar 13, 2008 7:54 am
Hey hey guys - netigen & torontogmat.com - I am not getting the thing. Yop! I agree with netigen. The answer should be C. How come should E be the answer to chose? I am not getting.
Guys can you pls explain it in little bit detail? Pls!
Correct me If I am wrong


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Amitava

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by torontogmat.com » Thu Mar 13, 2008 8:02 am
Scenario 1: Leslie loses 99.99% of her, say, $100 in the first year, leaving her with a penny, which she gains 140% on in the second year, leaving her with 2.4 pennies. Kerry makes 5% and 5%, and makes more money.

Scenario 2: Kerry loses 99.995% of her $200, leaving her with a penny. Leslie makes 20% and 20%.

different results obtained using information from both statements. E.

Whenever permissible, I like to pick extreme cases, as they often quickly show a pattern or trick.

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by camitava » Thu Mar 13, 2008 8:08 am
torontogmat.com, thanks for ur explanation. Got it now. But is it not little awkward? I mean it appears to me little awkward... :cry: :wink:
Correct me If I am wrong


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Amitava

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by torontogmat.com » Thu Mar 13, 2008 8:17 am
well, it may very well be awkward. I suppose I could have picked some more reasonable numbers :)

however, as I said, I do this on purpose. number picking is definitely more of an art than a science, but if you look at your options, there is often some scenario that greatly simplifies your work.

some people are smart, and can solve questions the complicated way. I prefer to be lazy ;)