Please further explain MGMAT's explanation

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

Redeem

This topic has expert replies

Post new topic Post Reply

Previous Topic Next Topic

p2dski: Junior | Next Rank: 30 Posts; Posts: 18; Joined: Thu Aug 27, 2009 2:43 am

Please further explain MGMAT's explanation

by p2dski » Mon Aug 31, 2009 6:57 am

I could not figure this question out for the life of me. :roll: I ended up guessing.

MGMAT's explanation just confused me more. Could someone please elaborate on MGMAT's explanation?

Attached is the picture of the question (There is a diagram)

If C->D= (5^13-5^12), then how is 3 times that 6(5^13-5^12)?

I'm lost.

Attachments

"Patience, persistence and perspiration make an unbeatable combination for success." -Napoleon Hill

Quote

Source: Beat The GMAT — Problem Solving | Mon Aug 31, 2009 6:57 am

gmatcoach: Junior | Next Rank: 30 Posts; Posts: 15; Joined: Sun Aug 23, 2009 6:58 am; Thanked: 1 times; GMAT Score:770

by gmatcoach » Mon Aug 31, 2009 7:32 am

distance D-C = L = 5^13 - 5^12 = 5^12(5-1) = 5^12(4).

C - A = 2xL => A = C - 2L = 5^12 - 5^12(4)(2) = 5^12(1-8) = -7x5^12. So D is the answer

Quote

p2dski: Junior | Next Rank: 30 Posts; Posts: 18; Joined: Thu Aug 27, 2009 2:43 am

by p2dski » Mon Aug 31, 2009 1:12 pm

Thanks Coach,

Why does 5^13 - 5^12 = 5^12(5-1)?

After putting it into the calculator I know they do, but how do you draw that conclusion?

"Patience, persistence and perspiration make an unbeatable combination for success." -Napoleon Hill

Quote

gmatcoach: Junior | Next Rank: 30 Posts; Posts: 15; Joined: Sun Aug 23, 2009 6:58 am; Thanked: 1 times; GMAT Score:770

by gmatcoach » Tue Sep 01, 2009 3:39 am

5^13 - 5^12 = 5^12(5-1) because :

Just split the powers:
5^13 = (5^12)(5)
5^13 - 5^12 = (5^12)(5)-5^12(1) (factor the powers: so they have 5^12 as a common factor)
= 5^12(5-1)

Quote

bharathh: Master | Next Rank: 500 Posts; Posts: 159; Joined: Thu Aug 27, 2009 10:30 am; Thanked: 19 times

by bharathh » Tue Sep 01, 2009 5:50 am

What level of question was this? 700-800 or less? Was a fun question to solve.

Any time you see exponents try to get them to the same power just as you would try to get an algebraic equation expressed in terms of one variable. It helps a lot!