A certain sum of money is invested at 10%. Twice that amount is invested at 8%. The total amount of interest from both investments is $91. how much is invested at 8%.

Question

amistre64 · Answer

Hmmm.... interest is Money times %.  So if we say x(10%) + 2x(8%) = 91 we should be able to solve for x.

x(.1) + 2x(.08) = 91
x(.1 + 2(.08)) = 91
x(.1 + .16) = 91
x(.26) = 91
x=350  and 2x = 700.

Double check:

350(.1) + 700(.08) = 91
35 + 56 = 91
91 = 91 ...  yay!!!

700 was invested at 8%.  If I did it correctly that is :)
x = 91/.26 = 9100/26

x=