James B. answered • 06/07/16

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Let X = amount invested at 6%

Let x + 3000 = amount invested at 9%

Interest Formula:

I = Prt

For our scenario, time t is 1 year

FOR 6% INVESTMENT

I = x • .06 • 1

= .06x

FOR 9% INVESTMENT

I = (X + 3000) • .09 • 1

= .09X + 270

The combined interest is $4170

We can construct the following equation:

Interest at 6% + Interest at 9% = 4170

.06x + .09x + 270 = 4170

.15x + 270 = 4170

.15x = 3900

x = 26,000

Thus $26,000 is invested at 6% and $29,000 is invested at 9%