Help needed with Remainder Question

Expert replies

SM2010: Junior | Next Rank: 30 Posts; Posts: 19; Joined: Sun Jun 06, 2010 9:40 am; Thanked: 4 times

by SM2010 » Tue Jun 15, 2010 6:47 am

Hi. Can someone please show me how to do the following question:

If r is the remainder when the positive integer n is divided by 7, what is the value of r?

(1) When n is divided by 21, the remainder is an odd number

(2) When n is divided by 28, the remainder is 3

Like this post

Source: Beat The GMAT — Data Sufficiency | Tue Jun 15, 2010 6:47 am

mj78ind: Master | Next Rank: 500 Posts; Posts: 265; Joined: Mon Dec 28, 2009 9:45 pmFollowed by: 2 members; Thanked: 26 times; GMAT Score:760

by mj78ind » Tue Jun 15, 2010 7:00 am

Let's look at stmt 1, say n = 45 remainder with 21 = 3, remainder with 7 = 3; say n = 51, remainder with 21 is 9, with 7 it is 2. hence 1, not sufficient.

Stmt 2 n = 28*x + 3, where x is an integer. This can also be written as n = 4*(7*p) + 3, we know that 28*x is always divisible by 7, hence whatever remainder remains from 28 will also remain from 7.
This can be verified by picking numbers like 31, 59, 87 etc..

Hence answer is B.

OA please?

Like this post

selango: Legendary Member; Posts: 1460; Joined: Tue Dec 29, 2009 1:28 amFollowed by: 7 members; Thanked: 135 times

by selango » Tue Jun 15, 2010 7:11 am

n=7q+R

What is R?

n=21q+r

n can be any number like 22,24,26.insufficient

n=28q+3 can be rephrased as,

n=7(4q)+3

from this when n is divisible by 7,the remainder will be 3.

n=31,59,67,95

Hence B

Like this post

SM2010: Junior | Next Rank: 30 Posts; Posts: 19; Joined: Sun Jun 06, 2010 9:40 am; Thanked: 4 times

by SM2010 » Tue Jun 15, 2010 7:23 am

Thanks very much guys! B is indeed the correct answer.....

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

560 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (560 Reviews)

"Target Test Prep is the closest to the official version of the GMAT exam, about 99% accuracy in terms of the quality and quantity of information. The course has excellently created singular sets of focused lessons and tests for every possible topic that one could come across in the official GMAT exam."

"The TTP course maximizes the efficiency of the time you spend studying. It will take time and effort but I could almost guarantee that if you complete the course exactly as it is laid out you will get an amazing score. They also have a very responsive team willing to help with any questions you might have."

"TTP has two things that I think no other test prep company offers: A teaching approach that reinforces understanding and an attitude that will give you the mental preparedness needed to succeed on the test. TTP gives you a deep understanding of the concept you need to know while teaching you how to think."

Write a Review