DS

[gmatmachoman]

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!

[albatross86]

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.

[selango]

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

[albatross86]

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!

[selango]

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

[albatross86]

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

[selango]

Oops my silly mistake.Now edited it.

ur always ahead of me in answering the question

[akhpad]

Yup, I agree on B.

[Testluv]

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.

[sumanr84]

Refer Papgust flash card and u can answer within secs.

Weighted Averages:

https://www.beatthegmat.com/papgust-s-gm ... 02-45.html