how much did he invest at 14%?

Question

Bob invested $20,000, part at 14% and part at 13%. If the total interest at the end of the year is $2,720

Answer 1

Assume simple interest: I = PRT
X = Amt at 14%
20,000 - X = Amt at 13%
Int 1 = X(.14)(1) = .14X
Int 2 = (20,000 - X)(.13)(1) = 2600 - .13X
Int 1 + Int 2 = 2720
.14X + 2600 - .13X = 2720
.01 X = 120
X = 12,000
and 8,000 invested at 13%

Answer 2

Let me see

Suppose he invested x amount at 14% and therefore he invested 20000-x at 13%

Is it simple interest or compound interest? Probably compound, knowing how sadistic your maths teacher will be.

CI

At = A0 (1 + R/100)^t

At 1 year, amount at 14% and 13% are

A1 = x(1+14/100)^1 + (20000-x)(1+13/100)^1

And of course A1 - A0 is your interest (2720)

So solve for x

Answer 3

.14x + .13(20,000-x) = 2720
.14x + 2600 - .13x = 2720
.01x= 120
x = 12,000
20,000-x = 8,000