Question

You invested $18,000 in two accounts paying 7% and 9% annual interest, respectively. If the total interest earned for the year was $1560, how much was invested at each rate?

Answer 1

hi

Let call money invested at 7% "X " and money at 9 % "Y" .

7% = 7/100 = 0.07

9% = 9 /100 = 0.09

So X+Y = 18 000

0.07X + 0.09Y = 1560

So if : X+Y = 18 000

Y = 18 000 -X

then

0.07X + 0.09 ( 18 000 -X ) = 1560

0.07X +0.09 * 18 000 - 0.09X = 1560

0.07X + 1620 -0.09X = 1560

0.07X-0.09X = 1560-1620

-0.02X = -60

X = -60 /-0.02

X = 3 000

If X = 3 000 then Y = 18 000 -3 000 = 15 000

Conclusion : 3 000 dollars were invested at 7 % and 15 000 at 9%

0.07* 3 000 = 210

15 000* 0.09 =1350

Total = 210+1350 = 1 560