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annoying GMAT prep question

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annoying GMAT prep question

by awilhelm » Sun Dec 14, 2008 8:39 pm
When a tree was first planted, it was 4 feet tall and its height increased at a constant rate for the next 6 years. At the end of 6 years, the tree was 1/5 taller than it was at the end of the 4th year. By how many feet did the tree increase each year?

What's the best way to attack this?

Thanks!
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by muzali » Sun Dec 14, 2008 8:55 pm
Set up an arithmatic progression:
a=4 (4ft tall to begin with)
d = rate of growth every year

End of 1st year, height = a+d
End of 2nd year, height = a+2d
End of 4th year, height = a+4d
End of 6th year, height = a+6d

it is given that a+6d = (6/5)(a+4d)

we know a, solve for d to get the answer.
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by awilhelm » Sun Dec 14, 2008 9:19 pm
Thanks a lot.
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