Can anyone provide insight on how to solve the problem below? It comes from GMAT Prep Software.

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) ½
D) 2/3
E) 6/5


The correct answer is (D), but what is the correct method?

thanks

The height of the tree increased by a constant rate every year for next 6 yrs. Assume the increase in the height each year be 'x'. At the end of 6th yr the tree is 1/5th taller than it was at the end of 4th yr so the following equation can be set: -

Height of Tree at the end of 6th yr = Height of the Tree at the end of 4th + 1/5(Height of the tree at the end of 4th yr)

placing the absolute values in the equestion: -

4+ 6x = 4+4x + 1/5(4+4x)

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

20 + 30x = 24 + 24x
6x = 4

x = 4/6 or 2/3


Hope it helps.

Thanks
GMAT 2007

Also check out the below thread for another explanation (very similar, just more steps spelled out)
http://www.manhattangmat.com/forums/gmatprep-exam-1-question-31-t646.html?highlight=certain%20tree