Hi guys, this was written before I saw the post on how to write mathematically correct in the forum.

DS #90:

What is the value of x / yz ?

1. x=y/2 and z=2x/5
2. x/z=5/2 and 1/y=1/10


My question about this problem has to do with part 1. The question is fairly simple: Why in part 1 can’t I make all signs match up and equal x? x/yz would then look like this in the way I did it: x / 2x*2x/5.

Here is what the book says:

(1) From this, z can be expressed in terms of y by substituting y/2 for x in the equation z=2x/5, which gives us z=2(2/5) / 5= y/5. The value of x/yz in terms of y is then y/2 / y(y/5) = y/2(5/y[squared])=5/2y. This expression cannot be evaluated further since no information is given about the value of y; not sufficient. (BCE).


Here is how I did it:

What I did is take x=y/2 and make it 2x=y (which Quant book did not do), which then gave me: x / 2x*2x/5, which gave me x / 4x/5, which equals 5x / 4x, and I get 5/4. Meaning I mark this as AD and move to part 2.



Part 2 is easier to solve because we just plug in: y=10, x=5, z=2. 5/10*2=1/4, for which I pick letter D as my answer because both solutions by them selves are sufficient.


One of the big problems I see with my answer is that in part 1 I got 5/4, and in part 2 I got ¼, which is a contradiction and according to MGMAT, I did something wrong.

Please explain this problem and let me know whether and if so, then why I am wrong.

Thanks,

FinanceGuy25

we can write z = 2y/10

x = y/2

then (y/2) / ((y*y)/5) = 5/2y

so A is insufficient