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Q from GMATPrep test 1

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jonas
 Post subject: Q from GMATPrep test 1
 Post Posted: Tue Jun 03, 2008 8:33 am 
this question appeared on Free GMATPrep test 1.

Q: 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.

Answers:

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

test says 2/3 is correct answer. how is it possible to get this answer? and is it really correct?
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Nagm
 Post subject:
 Post Posted: Tue Jun 03, 2008 12:38 pm 
Q: 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.

Height of Tree at any year is given by following formula
H = 4 + KT, K = constant, T number of years.
Solve this equation for 4 & 6 years and find value of K.
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jonas
 Post subject:
 Post Posted: Wed Jun 04, 2008 7:57 am 
thanks. that was easy. i did not read the question carefully enough :(
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Success
 Post subject: Solution
 Post Posted: Wed Jun 04, 2008 8:02 am 
Taking a cue from the solution posted above

4+6k=Height of tree after 6 years
4+4K= Height of tree after 4 years
1/5(4+4K)= Incerase in height of tree from the 4th year to 6th year.

Thus: 4+6k = (4+4k) + 1/5(4+4K)
4+6k = 4+4K+4/5+4/5K
6K-4K-4/5K= 4-4+4/5
6/5k=4/5
k= 4/5 * 5/6
K=2/3
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rfernandez
 Post subject:
 Post Posted: Fri Jun 06, 2008 4:33 am 
Offline
ManhattanGMAT Staff


Posts: 386
Good to see everyone helping each other out. Nice solutions.
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