When a certain tree was first planted

[sanjay]

GMAT prep test-1.
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 6th year, the tree was 1/5 taller than it was at the end of 4th year. By how many feet did the height of the tree increased each year?

A. 3/10
B. 2/5
C. 1/2
D. 2/3
E. 6/5

OA is D.

Seems so easy, though. I tried hard, but unable to figure out the equation for the problem. Some one please help me figure it out.

Thanks
Sanjay

[alok.sarsidharan]

Let the increase per year = x

Therefore, height of the tree at the end of the 6th year is : 4 + 6x

Also, it is given that : At the end of 6th year, the tree was 1/5 taller than it was at the end of 4th year.

Height of the tree at the end of the 4th year = 4 + 4x

The tree was 1/5 taller than it was at the end of 4th year can be translated as follows :

[4 + 4x] + [1/5 (4+4x)]

Therefore ,
4 + 6x = [4 + 4x] + [1/5 (4+4x)]
Solve for x, answer is 2/3.

[sanjay]

Thanks Alok,

I realized the mistake I was making in doing such a small calculation. Some times you are so caught up with the figure, that your mind does not take any figure, but the wrong figure..

[Ben Ku]

Good explanation, Alok!