GMAT Prep 2 - Quant 1

This topic has expert replies
Senior | Next Rank: 100 Posts
Posts: 30
Joined: Thu Mar 22, 2007 8:53 pm
Thanked: 1 times

GMAT Prep 2 - Quant 1

by Sumit69 » Sat Apr 11, 2009 8:59 am
Please help me with solution.
Attachments
Quant 3.doc
(73 KiB) Downloaded 135 times

Legendary Member
Posts: 2467
Joined: Thu Aug 28, 2008 6:14 pm
Thanked: 331 times
Followed by:11 members

by cramya » Sat Apr 11, 2009 6:04 pm
Stmt I

This tells us that m and p are even since they both share a common factor 2

even/even we always get a even remiander if there is a remainder. We know the remiander is not 0 and it cant be 1 so it has to be greater than 1

SUFF

StmtII

x=5 y=6 REMAINDER > 1 NO
x=10 y=15 REMAINDER > 1 YES

INSUFF

A

Senior | Next Rank: 100 Posts
Posts: 38
Joined: Fri Feb 20, 2009 8:45 am
Thanked: 5 times

stuck at stmt 2

by syr » Sat Apr 11, 2009 6:04 pm
Given :
m, p integers &
2 < m < p &
p/m = NQ + r ; N - integer, Q - quotient, r - remainder

Is r > 1 ?

Stmt 1)

GCD (m,p) = 2
Plugging numbers -
m p
GCD( 4, 6) = 2
GCD( 8, 10) = 2
So, m, p have to be consecutive even integers for GCD to be 2 & m not a factor of p. Hence, r = 2.
Stmt 1) sufficient.

Stmt 2)
LCM(m, p ) = 30
Plugging numbers -

LCM( 5, 6) = 30
LCM( 3, 10) = 30
So, r = 1

I guess this is what even Sumit arrived at. I see that the OA is A). So we need to find which combination is not satisfying [ LCM(m,p) as 30 and r = 1] .

Experts, opinions please.

Senior | Next Rank: 100 Posts
Posts: 38
Joined: Fri Feb 20, 2009 8:45 am
Thanked: 5 times

by syr » Sat Apr 11, 2009 6:08 pm
Thanks cramya :)

10, 15... this was the combination !!

But, can you please tell me how you arrived at the combination 10,15 ? Is there an easier way to determine this ?

I could get only (3,10) & (5,6).

Legendary Member
Posts: 2467
Joined: Thu Aug 28, 2008 6:14 pm
Thanked: 331 times
Followed by:11 members

by cramya » Sat Apr 11, 2009 6:43 pm
Look at the possible combinations of factors of 30

30 = 2*3*5

2*5 = 10
3*5 = 15

General Tip:

For number properties questions try factorizing whats given in to their prime factors. This way its easier to see the connections.It will more often help than not.

Good luck, Syr.

Regards,
CR

Legendary Member
Posts: 1578
Joined: Sun Dec 28, 2008 1:49 am
Thanked: 82 times
Followed by:9 members
GMAT Score:720

by maihuna » Sat May 09, 2009 11:35 am
Good trick to note here is Even divides Even leaves remainder as even: any mathematical concept to proove this, Ian please?

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 2621
Joined: Mon Jun 02, 2008 3:17 am
Location: Montreal
Thanked: 1090 times
Followed by:355 members
GMAT Score:780

by Ian Stewart » Sun May 10, 2009 9:41 am
maihuna wrote:Good trick to note here is Even divides Even leaves remainder as even: any mathematical concept to proove this, Ian please?
Yes, that's certainly true. From the definition of quotients and remainders, when you divide n by d, we have

n = qd + r

where r is the remainder, and q is the quotient. You could rewrite the above:

r = n - qd

and if n is even, and d is even, then r must be even (since on the right side, we have even - even = even).

It's often easier to understand these types of abstract equations by plugging in a few numbers to see how they work.
For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

ianstewartgmat.com