% of % -- tough one

[2010gmat]

Is x% of x% of y equal to x% less than y ?

(1) x(x + 100) = 10,000
(2) y(y + 1) = 1

can anyone phrase the eqn for me??

is it

x/100*x/100*y = y - x/100

or is it

x/100*x/100*y = y-x/100*y {in this case shouldn't the question read as: Is x% of x% of y equal to x% of y less than y?


OA to follow

[palvarez]

Is x% of x% of y equal to x% of y less than y?

Oh well, it is a verbose way of saying the same thing.

x is 40% less than y ==> x is 60% of y.
x is 50 more than y ==> x = y + 50
x is 1/3 more than y ==> x = 4y/3
x is 1/3 less than y ==> x = 2y/3
x is 50 less than y ==> x = y - 50.

The translation, it appears, depends upon whether the number is a fraction or not. 50 is not a proper fraction; however, 40%, 50%, 1/3 are proper fractions.

proper fractions call for different interpretation.

x% less than y = (1-x%)y
x%*x%*y < (1-x%)y

or

x%x% < 1-x%

or

x%(1+x%) < 1
x(x+100) < 100^2

Answer is A.

[2010gmat]

Thanks a lot dude...that explanation helped me a lot...

I think we need good RC skills to tackle even the quant section...{seems like Whole of the GMAT is RC and am paying too little attention to RC...

[palvarez]

Thanks a lot dude...that explanation helped me a lot...

I think we need good RC skills to tackle even the quant section...{seems like Whole of the GMAT is RC and am paying too little attention to RC...

I betcha. That's one way to catch weak souls off guard on their GMAT rituals. Overlapping sets is another place you gotta be careful: focus on the object of the preposition "of", put that object in the denominator.

It appears that GMAT is drifting away from pure algebraic stuff, unless these algebraic questions--which involve absolute values, inequalities, and numbers-- are tough, to word problems.

They have a reason to do so: that's one way to punish non-native speakers with good math background.

I also suspect why GMAT has shifted focus on inequalities, numbers, absolute values. Indian math curriculum don't focus on these aspects much. I have seen Russian math books focusing on these topics.

[Testluv]

Thanks a lot dude...that explanation helped me a lot...

I think we need good RC skills to tackle even the quant section...{seems like Whole of the GMAT is RC and am paying too little attention to RC...

I betcha. That's one way to catch weak souls off guard on their GMAT rituals. Overlapping sets is another place you gotta be careful: focus on the object of the preposition "of", put that object in the denominator.

It appears that GMAT is drifting away from pure algebraic stuff, unless these algebraic questions--which involve absolute values, inequalities, and numbers-- are tough, to word problems.

They have a reason to do so: that's one way to punish non-native speakers with good math background.

I also suspect why GMAT has shifted focus on inequalities, numbers, absolute values. Indian math curriculum don't focus on these aspects much. I have seen Russian math books focusing on these topics.

Hi palvarez,

The test-maker does not make decisions on what topics are tested and how they are tested by reference to how a sub-pool would best be hurt. If the test-maker really wanted to hurt non-native speakers, there are many other things it could do to achieve that goal more effectively.

The GMAT has always tested verbal skills in quant (and quant skills in verbal). Absolute value, inequalities, etc have always been traditional staple topics tested on the GMAT.

[palvarez]

Thanks a lot dude...that explanation helped me a lot...

I think we need good RC skills to tackle even the quant section...{seems like Whole of the GMAT is RC and am paying too little attention to RC...

I betcha. That's one way to catch weak souls off guard on their GMAT rituals. Overlapping sets is another place you gotta be careful: focus on the object of the preposition "of", put that object in the denominator.

It appears that GMAT is drifting away from pure algebraic stuff, unless these algebraic questions--which involve absolute values, inequalities, and numbers-- are tough, to word problems.

They have a reason to do so: that's one way to punish non-native speakers with good math background.

I also suspect why GMAT has shifted focus on inequalities, numbers, absolute values. Indian math curriculum don't focus on these aspects much. I have seen Russian math books focusing on these topics.

Hi palvarez,

The test-maker does not make decisions on what topics are tested and how they are tested by reference to how a sub-pool would best be hurt. If the test-maker really wanted to hurt non-native speakers, there are many other things it could do to achieve that goal more effectively.

The GMAT has always tested verbal skills in quant (and quant skills in verbal). Absolute value, inequalities, etc have always been traditional staple topics tested on the GMAT.

I shoulda put it differently. (a) Some questions are difficult to all pools: inequalities, numbers, absolute values fall in this group. (b) Some questions are easy for one sub pool, but not for another pool. (c) There are word problems, which are difficult for all pools--whether native speakers or not; that for different reasons: for native speakers, it is an algebraic issue; for non-natives, it is a translation issue.

Taken together, questions of (a) and (c) are found to be statistically significant.

[Testluv]

Hi palvarez,

Yes, I think I agree with what you just wrote.

Both individuals and pools of individuals will naturally have varying profiles of strengths and weakenesses.

Accordingly, different individuals and pools will find different topics easier or harder, and different individuals and pools may find a particular topic difficult for different reasons.

Of course, none of this means that the GMAT is trying to make life harder for a certain individual or for a certain pool of individuals!