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 Author: Gennadiy [ Thu Aug 05, 2010 6:00 am ] Post subject: GMAT Algebra Let d > c > b > a. If c is twice as far from a as it is from d, and b is twice as far from c as it is from a, then(d – b) / (d – a) =A. 2/9B. 1/3C. 2/3D. 7/9E. 3/2The correct answer is D.Geometrical and algebraic solutions are below.

Author:  Gennadiy [ Thu Aug 05, 2010 6:20 am ]
Post subject:  Re: math: algebra, number line

Since the exercise mentions a number line, draw one. Since d > a, label the left end of the number line with d and the right end with a. The values of b and c will be between a and d:

Start with the relationship between c, a, and d. Since c is twice as far from a as it is from d,
the segment between a and d is divided into 3 pieces – two pieces between c and a and one piece between d and c. Each piece is 1/3 of d to a.

The relationship between b, c, and a says that b is twice as far from c as it is from a. This
means the segment between a and c is divided into 3 pieces.

The segment between c and a was 2/3 of the segment between d and a. Dividing 2/3 into 3 pieces makes each piece (2/3) / 3 = 2/9.

So d – b (the length of the segment between d and b) makes 7/9 of d – a (the length of the segment between d and a).