tree with constant growth

[poonamchiK]

Tree 1st planted was 4 feet tall. The height icreased a constant amount each yr for 6 yrs. If at the end of the 6th yr, tree was 1/5th taller than it was at the end of 4th yr, y how many feet did the height of the tree increase each yr?
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a.3/10
b. 2/5
c. 1/2
d. 2/3
e. 6/5

ans: 2/3
source: prep software

[jiteshshah00]

This is a linear growth problem and can be solevd by the equation y=mx+b, where m = growth rate (and this is what we have to find here), x= time and b = value at time zero.

Therefore at 4 year:
y = 4m+4

At 6 year:

y = 6m + 4

It says at 6 year it was 1/5 taller than 4th, so:

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

Solve tis and you will get m =2/3

[RonPurewal]

this problem is answered here:
when-a-certain-tree-was-first-planted-it-was-4-feet-tall-t646.html