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

Redeem

Integer confusion

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
User avatar
Senior | Next Rank: 100 Posts
Posts: 40
Joined: Sun Dec 28, 2008 2:52 am
Location: Denver
Thanked: 2 times

Integer confusion

by deagez » Sat Apr 11, 2009 3:50 am
If the two-digit integers M and N are positive and have the same digits, but in reverse order, which of the following CANNOT be the sum of M and N?

A) 181
B) 165
C) 121
D) 99
E) 44

The explanation made this problem more confusing than it originally was.
Help plz.

OA is A
Top
Source: — Problem Solving |
Legendary Member
Posts: 683
Joined: Tue Jul 22, 2008 1:58 pm
Location: Dubai
Thanked: 73 times
Followed by:2 members

by mals24 » Sat Apr 11, 2009 4:06 am
A 2 digit integer can be written in the following way: 10a+b; where a is the 10ths digit and b the units digit.
For instance: 21 = 10*2 + 1

So let M = 10a+b
and N = 10b+a (reverse the 10ths and units digit of M).

M+N = 11a+11b
= 11(a+b)

Hence the sum of M and N should be divisible by 11.

Only A doesn't fit the bill.
Top
Post new topic Post Reply
• Page 1 of 1