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When a certain tree was planted

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guest612
 Post subject: When a certain tree was planted
 Post Posted: Sat Apr 19, 2008 12:06 pm 
When a certain tree was planted, it was 4 ft 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

Answer: D. 2/3

Can you please tell me how to solve this problem? Also, can you help clarify if I'm calculating for 6 years or 7 years (because starting with Year 1 + 6 years)? I tried doing something along the lines of

year 4 =x
year 6 = x+(1/5)x
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tmmyc
 Post subject:
 Post Posted: Tue Apr 22, 2008 8:15 pm 
When the tree was planted, it was 4 feet tall. It then grows by a constant amount each year for 6 years. Call this constant amount 'x'.

Now: 4
1 year: 4+x
2 years: 4+2x
3 years: 4+3x
4 years: 4+4x
5 years: 4+5x
6 years: 4+6x

At the end of the 6th year, it was 1/5 taller than at the end of the 4th year. This means the 6th year height is 6/5 times the 4th year height (1 + 1/5 = 6/5).

(6/5)*(4+4x) = 4+6x

Solving for x, you get 2/3. The trees grows by 2/3 every year.
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RonPurewal
 Post subject:
 Post Posted: Thu Apr 24, 2008 3:57 am 
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ManhattanGMAT Staff


Posts: 7146
tmmyc wrote:
When the tree was planted, it was 4 feet tall. It then grows by a constant amount each year for 6 years. Call this constant amount 'x'.

Now: 4
1 year: 4+x
2 years: 4+2x
3 years: 4+3x
4 years: 4+4x
5 years: 4+5x
6 years: 4+6x

At the end of the 6th year, it was 1/5 taller than at the end of the 4th year. This means the 6th year height is 6/5 times the 4th year height (1 + 1/5 = 6/5).

(6/5)*(4+4x) = 4+6x

Solving for x, you get 2/3. The trees grows by 2/3 every year.


splendid.
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guest612
 Post subject: thank you
 Post Posted: Thu Apr 24, 2008 12:08 pm 
thank you both tymmc and ron. why do the questions seem harder? =(
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rfernandez
 Post subject:
 Post Posted: Thu Apr 24, 2008 5:30 pm 
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ManhattanGMAT Staff


Posts: 386


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