I would go for (D)
Taking first option =>
Let the investment with SI (8 pc) be X
then, investment with SI (6 pc) = 10K-X
thus, total SI on 10 K investment can be calculated by SI = (P*R*T)/100
i.e. (8*X*1)/100 + ((10K-X)*6*1)/100 = 640
=> X = 2K
thus, investment with SI (6 pc) = 10K - 2K = 8K
Now, considering second option =>
Suppose dollar value of investment with SI (8 pc) = X
then, dollar value of investment with SI (6 pc) = 4X
thus making 5X = 10K => X = 2K
thus, SI on dollar value of investment with SI (8 pc) would be:
(8*X*1)/100 = $160
Thus, each stmt alone is sufficient to answer the question. hence (D)
