Quant- gmat prep

[its.ur.life]

When a 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.

1. 3/10
2. 2/5
3. 1/2
4. 2/3
5. 6/5

Ans:2/3

Acc to me.
Let height after 4 years = x
Height after 6 years = 6/5 * height after 4 years.
x * (1*R/100)^2 = 6/5 * x
(1*R/100)^2 = 1.2

if we approximate this than 1.1 * 1.1 = 1.21.
So r = 10 %

Lets calculate height after 1st year.
4 * 1.1 = 4.4

So increase in height in 1 year is 4.4 -4 =0.4 ft.

So ans according to me is 0.4 feet.

KJ

[tim]

the problem is that you are assuming a constant RATE of growth (10% per year) rather than a constant linear growth. in other words, you should be adding a constant each year rather than multiplying by a constant each year. try the problem again with this information and see if that helps..