Question

Walter invests $12,000, part at 7% annual interest and part at 8.5% annual interest. How much is invested at each rate if Reggie's total annual interest is $900?

Answer 1

for 7% , $8,000

for 8.5%, $4,000

Explanation:

Key amount at 7% be x and amount at 8.5% be y

Mathematically;

x + y = 12,000 ••••••(i)

Let’s now work

with the interest;

7% of x + 8.5% of y = 900 ••••••(ii)

0.07x + 0.085y = 900

So we have two equations to solve simultaneously

From 1, x = 12,000-y

Substitute this into ii

0.07(12000-y) + 0.085y = 900

840-0.07y + 0.085y = 900

0.015y = 900-840

0.015y = 60

y = 60/0.015

y = 4000

x = 12000-4000

x = $8,000