GMAT PREP I TREE

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pkw209: Master | Next Rank: 500 Posts; Posts: 266; Joined: Mon Oct 19, 2009 9:46 pm; Thanked: 8 times; GMAT Score:690

GMAT PREP I TREE

by pkw209 » Wed Dec 30, 2009 3:56 pm

Hi,

I solved this question through backsolving but was hoping someone could explain this one algebraically. FYI, I got this from Zuleron's list of 198 gmat prep questions. The answer is D. Thanks!

97) When a tree was planted it was 4 feet. Its height increased by a constant amount each year for 6 years. After 6 years the tree was 1â�„5 taller than at the end of 4th year. By how many feet did the height of the tree increase each year?

a. 3â�„10
b. 2â�„5
c. 1â�„2
d. 2â�„3
e. 6â�„5

Quote

Source: Beat The GMAT — Problem Solving | Wed Dec 30, 2009 3:56 pm

ace_gre: Senior | Next Rank: 100 Posts; Posts: 98; Joined: Mon Nov 23, 2009 2:30 pm; Thanked: 26 times; Followed by:1 members

by ace_gre » Wed Dec 30, 2009 4:55 pm

Let the amount gained by the tree each year be x.

So end of 1st year tree is 4+x
end of 2nd year tree is 4+2x...end of 6th year tree is 4+6x.

Also given 4+6x = 1 1/5*(4+4x).
Solving for x = 2/3.