Question

Katie invested a total of ​$4000​, part at 2​% simple interest and part at 3​% simple interest. At the end of 1​ year, the investments had earned ​$90 interest. How much was invested at each​ rate?

Answer 1

$3000

$1000

Explanation:

the formula for simple interest = principal x time x interest rate

let the amount invested in the 2% investment be a

let the amount invested in the 3% investment be (4000 - a)

(a x 0.02 x 1) + ([4000 - a] x 0.03 x 1) = $90

0.02a + 120 - 0.03a = 90

Collect like terms and solve for a

0.01a = 30

a = $3000

The amount invested in the 3% investment be (4000 - a) = $4000 - $3000 = $1000