The value of two digit integer

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yass20015: Senior | Next Rank: 100 Posts; Posts: 38; Joined: Fri Aug 07, 2015 3:06 am; Thanked: 1 times

by yass20015 » Mon Aug 10, 2015 11:45 am

What is the value of the two-digit positive integer n?
1- The sum of the digits in n is 12
2- If the digits in a are reversed, the value of the number formed is 36 more than the value of n.

The answer is C)Together. But why not B ? Why the statement 2- alone is not enough ? Can we found other numbers than 84 and 48 ?

Thanks

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Source: Beat The GMAT — Data Sufficiency | Mon Aug 10, 2015 11:45 am

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Brent@GMATPrepNow: GMAT Instructor; Posts: 16207; Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members; Location: Vancouver, BC; Thanked: 5254 times; GMAT Score:770

by Brent@GMATPrepNow » Mon Aug 10, 2015 12:01 pm

yass20015 wrote:What is the value of the two-digit positive integer n?
1- The sum of the digits in n is 12
2- If the digits in a are reversed, the value of the number formed is 36 more than the value of n.

The answer is C)Together. But why not B ? Why the statement 2- alone is not enough ? Can we found other numbers than 84 and 48 ?

Thanks

How about 37 and 73?
Or 26 and 62?

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com

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Max@Math Revolution: Elite Legendary Member; Posts: 3991; Joined: Fri Jul 24, 2015 2:28 amFollowed by: 37 members; Location: Las Vegas, USA; Thanked: 19 times

by Max@Math Revolution » Thu Aug 20, 2015 10:08 am

In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem.
Remember equal number of variables and equations ensures a solution.

=> Since we have 2 variables (units digit and tens digit) in the original condition, we need 2 equations to solve the problem and thus the answer is C. (1) 1 equation, (2) 1 equation

=> 2) is not the answer because the number of n is NOT unique, NOT sufficient,

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