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by gmatmachoman » Sat Jun 26, 2010 10:40 pm
A group of men and women competed in a marathon. Before the competition, each competitor was weighed and the average weight of the female competitors was found to be 120 lbs, while the average weight of the men was found to be 150 lbs. What was the average weight of all of the competitors?

(1) 100 men competed in the marathon.
(2) There were twice as many men as women competing in the marathon


Yeah I agree its basic....but u guys can try out!
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Source: — Data Sufficiency |
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by albatross86 » Sat Jun 26, 2010 10:50 pm
This is weighted average. If no. of women is W and men is M, then the average weight of both men and women is given by 120*W + 150*M / (W + M)

So if we have the values of M and W it would be sufficient.


1. This only gives us the value of men. Insufficient.


2. M= 2W
Substitute in our eqn above.

120*W + 150*2*W / ( W + 2W)
= 60*W*(2 + 5) / 3*W
= 20*7
= 140

We needn't have even solved it, because we see that W cancels out so we can actually find an answer. Sufficient.

B.
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by selango » Sun Jun 27, 2010 3:30 am
Sum of female comp/F=120

Sum of male comp/M=150

Average of all comp=120F+150M/F+M

From stmt1,M=100

Insufficient.

From stmt2,M=2F

sub M=2F in above equation and we can solve the equation.

Hence B
Last edited by selango on Sun Jun 27, 2010 3:40 am, edited 1 time in total.
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by albatross86 » Sun Jun 27, 2010 3:32 am
selango wrote:Sum of female comp/F=120

Sum of male comp/M=150

Average of all comp=120F+150M/F+M

From stmt1,M=100

Insufficient.

From stmt2,M=2F-->F=50

Combining we get,

120*(50)+150*(100)/100+50

Hence C

Hi selango,

Please see my explanation for Statement 2 above and see if you agree. Thanks!
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by selango » Sun Jun 27, 2010 3:36 am
yes albatross86. I agree with ur method.

Instead of substituting the values, u sub the variables.

This also seems to be quick way to solve :)
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by albatross86 » Sun Jun 27, 2010 3:37 am
selango wrote:yes albatross86. I agree with ur method.

Instead of substituting the values, u sub the variables.

This also seems to be quick way to solve :)
Thanks, the reason I asked is because you seem to have picked C, but as you can see from my explanation, B is sufficient. Perhaps you mistyped :)
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by selango » Sun Jun 27, 2010 3:43 am
Oops my silly mistake.Now edited it.

ur always ahead of me in answering the question :)
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by akhpad » Sun Jun 27, 2010 6:56 am
Yup, I agree on B.
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by Testluv » Sun Jun 27, 2010 10:49 pm
The number one skill in DS is NOT doing math!

Step 1 of the Kaplan method tells us to focus on the question stem, and determine what information would be necessary to answer the question (BEFORE going to the statements).

The question stem tells us the average weight of females and the average weight of males.

What information would be necessary to answer the question?...the relative quantities of males and females, ie, the ratio between males and females.

(1) doesn't give us what we need...insufficient. Eliminate A and D.

(2) gives us the relative quantities of males and females...sufficient.

Choose B.
Kaplan Teacher in Toronto
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by sumanr84 » Mon Jun 28, 2010 9:23 am
Refer Papgust flash card and u can answer within secs.

Weighted Averages:

https://www.beatthegmat.com/papgust-s-gm ... 02-45.html
I am on a break !!
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