interesting DS questions....from GMATPREP

[givinggmat]

1. x and y are positive integers. The value of xy?
(a) The GCD of X and Y is 10
(b) The LCM of X and Y is 180



2. Is sqrt(x-3)^2 = 3 - x ?
(a) x != 3
(b) -x|x| > 0


answers: C and B. Explaination would be helpful..

[sg_berries]

1) x> 0, y>0, value of xy = ?

(a) GCD of x and y = 10 not sufficient to find xy.

(b) LCM of x and y = 180 not sufficient to find xy.

combining the two: GCD(x,y) = (xy)/LCM(x,y) , hence xy = 10*180 = 1800 .

sufficient. answer C


(2) (x-3)^2 = |x-3| = x-3 {if (x-3) >0} or -(x-3) {if (x-3)<0}

(a) x!=3 not suffcient to answer

(b) -x|x| > 0
As we know that |x| > 0 therefore for -x|x| > 0 to fold true -x should be greater than 0. Which inturn implies that x should be negative i.e. x<0.

x<0 ====> x-3 is negative i.e. (x-3) <0 , hence |x-3| = -(x-3) = 3-x since (x-3)<0.

Answer B

[madboy]

In q # 2, statement 1 seems absurd.
Factorial is only defined for a positive integer and no integer has a factorial values of 3

[seahawk]

1> How about 90 and 20
answer E

[givinggmat]

Originally Posted by madboy

In q # 2, statement 1 seems absurd.
Factorial is only defined for a positive integer and no integer has a factorial values of 3

it is not Factorial... it is X NOT EQUAL TO 3

[sg_berries]

1) 90 and 20 GCD : 10 , LCM : 180 GCD * LCM = 1800 = 90*20 ... answer C