GMATPrep Tree Problem

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GMATPrep Tree Problem

by gmat8000 » Sun Oct 21, 2007 5:04 pm
I can't figure this damn problem out and I know the solution is easy.

When a certain tree was first planted it was 4 feet tall and the height of the tree increased by a constant amount each year for the next 6 years. At the end of the 6th year the tree was 1/5 taller than it was at the end of the 4th year. By how many feet did the height of the tree increase each year?

a) 3/10
b) 2/5
c) 1/2
d) 2/3
e) 6/5

The answer is D. Please provide the solution. Thanks.
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by ri2007 » Sun Oct 21, 2007 6:54 pm
Assume height increases by X feet in one year
At the end of year 4 height = 4 + 4X
At the end of year 6 height = 4 + 6X

Given (4+6X)-(4+4X) = 1/5(4+4X)
So 2X = 1/5 (4+4X)
So 10X = 4 +4X
So 6X = 4 and X = 2/3