How much was invested at each rate?

Question

you invested $9000 in two funds paying 4% and 7% annual interest. Athe end of the year, the total interest from these investments was $555. How much was invested at each rate?

Answer 1

Investment in 4% paying fund = x

 

so Investment in 7% paying fund = 9000-x

 

 

Interest on 4% paying fund =x* 4% = 0.04x

Interest on 7% paying fund =(9000- x)*7% =(9000-x)*0.07 =630-0.07x

 

So 

 

0.04x+630 -0.07x =555

 

-0.03 x +630 =555

 

-0.03x =- 75

 

x =2500

 

Investment in 4% paying fund = x = $ 2500

so Investment in 7% paying fund = 9000-x = $6500

Answer 2

I = prt

Interest = principal*rate*time

 

In this case the total interest will be the sum of

the interest earned at each rate.

 

If we invest $x at 4%, we invest 9000-x at 7%

 

555 = x(.04)(1) + (9000-x)(.07)(1)

555 = .04x - .07x + 630

555 = -.03x + 630

555-630 = -.03x

-75 = -.03x

 

x = -75/(-.03) = $2500 invested at 4%

 

9000-x = 9000- = $6500 invested at 7%