An investment of d dollars at k percent simple annual interest yields $600 interest over a 2-year period. in terms of d, what dollar amount invested at the same rate will yield $2,400 interest over a 3-year period?

so amount is 8d / 3 or 2.667 d

Explanation:

given data

invest amount = $d

rate r = k%

interest = $600

time t = 2 year

to find out

amount invested with interest #2400 for 3 year

solution

we will apply here interest formula that is

interest = principal × rate × time  / 100      1

put here value we get 2 equation

600 = ( d × k × 2 )  / 100    a

dk = 30000          2

and for 2400 interest for 3 year

2400 =  ( amount × k × 3 )  / 100   b

amount × k = 80000        3

so from equation 2 and 3  

amount × (3000/d) = 80000

amount = 8d / 3

so amount is 8d / 3