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A tree's growth rate?

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A tree's growth rate?

by phoenixhazard » Sat Dec 11, 2010 12:59 pm
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

OA: D
please explain the answer, i thought i had this one...
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by Bharat » Sat Dec 11, 2010 4:09 pm
Answer: D

H1 = 4 ft
let d be the change in height every year.
H4 = 4 + 4d
H6 = 4 + 6d
Given: H6 - H4 = (1/5)*H4
replace values in this equation from above & solve for d.
(4 + 6d) - (4 + 4d) = (1/5)*(4 + 4d)
2d = (1/5)*(4 + 4d)
10d = 4 + 4d
6d = 4 or d = 2/3

let me know if you have questions.

Regards,
Bharat.
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by phoenixhazard » Sat Dec 11, 2010 4:31 pm
Bharat wrote:Answer: D

H1 = 4 ft
let d be the change in height every year.
H4 = 4 + 4d
H6 = 4 + 6d
Given: H6 - H4 = (1/5)*H4
replace values in this equation from above & solve for d.
(4 + 6d) - (4 + 4d) = (1/5)*(4 + 4d)
2d = (1/5)*(4 + 4d)
10d = 4 + 4d
6d = 4 or d = 2/3

let me know if you have questions.

Regards,
Bharat.
ah crap, i set 1/5*(4+4d) = 4+6d didn't subtract the difference, thanks
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