Q from GMATPrep test 1

[jonas]

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?

[Nagm]

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.

[jonas]

thanks. that was easy. i did not read the question carefully enough :(

[Success]

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

[rfernandez]

Good to see everyone helping each other out. Nice solutions.