This is essentially an arithmetic progression.

Tn = a + (n-1)d

a = 4 (initial value)
d = increment
n = term (in this case its "year", n=1 means when the tree is planted)
Tn = value at the given nth term


T1 = a
T2 = a + d (after 1 year)
T3 = a + 2d (after 2 years)
T4 = a + 3d (after 3 years)
T5 = a + 4d (after 4 years)
T6 = a + 5d (after 5 years)
T7 = a+ 6d (after 6 years)

From the question, we know that:

T7 =(6/5)*T5
a + 6d = (6/5)*(a + 4d)
5*(a + 6d) = 6*(a + 4d)
5a + 30d = 6a + 24d
a = 6d
4 = 6d (we know that a=4)
d=2/3

Choose D

-BM-

Thanks Blumentor, but i just don't get one thing:
How do you go from:
T7 =(5/4)*T5

to:
a + 6d = (6/5)*(a + 4d)?

Baldini wrote:Thanks Blumentor, but i just don't get one thing:
How do you go from:
T7 =(5/4)*T5

to:
a + 6d = (6/5)*(a + 4d)?

I made a careless mistake. Thanks, I've corrected it in my earlier post.



-BM-