Please further explain MGMAT's explanation

[p2dski]

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.

[gmatcoach]

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

[p2dski]

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?

[gmatcoach]

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)

[bharathh]

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!

[gmatcoach]

this probably in the high 600's range