sagnik242 wrote:

Bunuel wrote:

Is y < 2x ?

(1) y/4 < x/2. Multiply both sides by 4: y < 2x. Sufficient.

(2) (y - 2x)/3 < 0. Multiply both sides by 3: y - 2x < 0. Re-arrange: y < 2x. Sufficient.

Answer: D.

Hope it's clear.

Wait when do we know we can multiply or allowed to do so in inequalities or simplify?

Hi,

you can always multiply or divide an equality/inequality by a constant number, may it be fraction,+ive or ,-ive..

But you cannot do the same by a variable like X, y etc..

the reason is we do not know the value of variable and it could be 0, but by dividing by a variable, we negate that possiblity..

4/x^2 > 4/x...

here you can eliminate 4 from both sides but not 1/x...

Hope it helps

_________________

1) Absolute modulus : http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372

2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html

3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html

GMAT online Tutor