Percentages/Weighted Average:

[mohit.khemu]

What fraction of this year's graduating students at a certain college are males?
1- of this year's graduating student, 33 % of the males and 20% of females transferred from another college.
2- of this year's graduating students 25% transferred from another college.

OA:C
Ron, this is from one of your other posts:
note that this is a WEIGHTED AVERAGES problem.
on weighted averages problems, if you know any 2 of the following 3, then you can find the third one:
1. the ratio of 'weights' of the different quantities
2. the values of the quantities
3. the weighted average

Can we do the above posted problem also by this concept? I had two similar questions in the same prep.

Thanks in anticipation.

[RonPurewal]

What fraction of this year's graduating students at a certain college are males?
1- of this year's graduating student, 33 % of the males and 20% of females transferred from another college.
2- of this year's graduating students 25% transferred from another college.

OA:C
Ron, this is from one of your other posts:
note that this is a WEIGHTED AVERAGES problem.
on weighted averages problems, if you know any 2 of the following 3, then you can find the third one:
1. the ratio of 'weights' of the different quantities
2. the values of the quantities
3. the weighted average

Can we do the above posted problem also by this concept? I had two similar questions in the same prep.

Thanks in anticipation.

yes.
the question is asking for the fraction of males; knowing the fraction of males is equivalent to knowing the ratio of males to females. therefore, the question is asking for #1 above.
statement 1 gives the values of the quantities (#2 above) and statement 2 gives the weighted average (#3 above), so, together, the are sufficient.

[mohit.khemu]

Thanks a lot. Really appreciate it.

[jnelson0612]

:-)

[ganeshgajamugan]

if you know any 2 of the following 3, then you can find the third one:
1. the ratio of 'weights' of the different quantities
2. the values of the quantities
3. the weighted average

I understand everything except the scenario when you are given the ratio of weights and the weighted average. How does one go about finding the values of the quantities? I am able to find the ratio of the quantities, but cannot find the exact quantities? I solved some questions backwards and tried omitting the values and seeing if they were solvable, but I ended up with many possibilities. However, the ratio of the values of quantities could be calculated... Could you confirm that the actual values of the quantities cannot be calculated or if they can, can you please explain how?

[RonPurewal]

if you know any 2 of the following 3, then you can find the third one:
1. the ratio of 'weights' of the different quantities
2. the values of the quantities
3. the weighted average

I understand everything except the scenario when you are given the ratio of weights and the weighted average. How does one go about finding the values of the quantities? I am able to find the ratio of the quantities, but cannot find the exact quantities? I solved some questions backwards and tried omitting the values and seeing if they were solvable, but I ended up with many possibilities. However, the ratio of the values of quantities could be calculated... Could you confirm that the actual values of the quantities cannot be calculated or if they can, can you please explain how?

ya, they can't. i was pretty much improvising when i wrote that, haha.

if you have the weights and the weighted average, what you can find is the relative distances away from the weighted average.
for instance, if 'p' has twice the weight of 'q' and the weighted average is 20, then 'p' must be exactly half as far away from 20 as 'q' (and in the opposite direction).
so, for instance, if q = 30 in this situation, then p = 15. or, if p = 30, then q = 0.

that was a stupid moment. heh.
it's interesting that it took about 2.5 years for someone to notice that something was wrong with that statement (which i think i posted in late 2009). nice catch.