BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

GMAT PREP Practice Test 2 DS

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Newbie | Next Rank: 10 Posts
Posts: 4
Joined: Fri Mar 09, 2007 1:16 pm

GMAT PREP Practice Test 2 DS

by joonwons » Mon Jul 23, 2007 9:33 pm
If X and y are positive integers, is xy a multiple of 8?
(1) The greatest common divisor of x and y is 10.
(2) The least common multiple of x and y is 100.

The answer is C. Can somebody please help me out?
Last edited by joonwons on Tue Jul 24, 2007 10:08 am, edited 1 time in total.
Top
Source: — Data Sufficiency |
Senior | Next Rank: 100 Posts
Posts: 65
Joined: Tue Jun 12, 2007 12:57 am

by erdnah » Tue Jul 24, 2007 1:26 am
let me try:
(1) x and y both are divisible by 2 and 5 (they have both the prime factors 2 and 5). this gives us no information if xy is divisible by 8.
(2) either x or y has got two times the prime factors 2. and the same or the other one has got two times the prime factor 5. this gives us no information if xy is divisible by 8.

taken both together, we can take a look at all prime factors together (x and y are multiplied!): 2, 2, 2, 5, 5, 5 .... since a number is divisible by the product of all its primes, the number must be divisble by 8 (2x2x2).
Top
Newbie | Next Rank: 10 Posts
Posts: 3
Joined: Mon Jul 23, 2007 4:52 pm

by rupam » Tue Jul 24, 2007 1:49 am
gcd . lcm = a.b
Top
Senior | Next Rank: 100 Posts
Posts: 62
Joined: Fri Jul 13, 2007 2:06 pm

by chatekar » Tue Jul 24, 2007 5:32 am
As correctly said by rupam,

To answer the question you need to know the value of product xy.
And to know the value of product xy, you need to konw its gcd and lcm
as xy = gcd * lcm

So we need both the statements

Thanks
Top
Post new topic Post Reply
• Page 1 of 1