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

Redeem

LCM and GCD

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Legendary Member
Posts: 621
Joined: Wed Apr 09, 2008 7:13 pm
Thanked: 33 times
Followed by:4 members

LCM and GCD

by vittalgmat » Wed Dec 16, 2009 8:26 pm
The least common multiplier of A and B is 120, the ratio of A and B is 3:4, what is the largest common divisor?

How do u attack this problem? .. what are the approaches to take.

[spoiler]OA: 10

We know that A * B = LCM * GCD and we now LCM = 120.
So we get A *B = 120* GCD.
Now how does the ratio of the two numbers play out.
Pls explain in detail

[/spoiler]
Top
Source: — Problem Solving |
User avatar
Senior | Next Rank: 100 Posts
Posts: 45
Joined: Sun Dec 28, 2008 2:17 am
Location: lahore, pakistan

by hamxa » Mon Jan 04, 2010 8:05 am
I will approach this in a different way:

factors of 120 = 2*2*2*3*5

now ratio of A and B is 3:4.
WHICH MEANS A=multiple of 3
and B = multiple of 4

Now: multiple of both has to be the same as its a ratio.
In 120 if we take out 3 and 4, we are left with the factors 2 & 5.

hence A and B should have 2 & 5 in them
A=3*10 =30
B=4*10 = 40

now GCD of 30 & 40 = piece of cake :)
Top
Post new topic Post Reply
• Page 1 of 1