Question

Interest earned=amount invested times rate of interest. Larry has an annual return of $213 from $3000 invested at simple intrest, some at 5% and the rest at 8% how much is invested at each rate?

Answer 1

i = prt
213 = .05x(1) + .08(3000-x)(1) if part of it is at 5% then the rest of the $3000 is at $3000 - x.... For example if x = 1000 then 3000-1000 would be the $2000 at the other rate
213 = .05x + 240 - .08x (Distributed to get this)
213 = -.03x + 240 (Added like terms)
-27 = -.03x (Subtracted 240 from both sides)
$900 = x (Divided by -.03 on both sides

So $900 at the 5% which would give you $45 and
$3000 - $900 = $2100 at 8% which would give you $168 which if you add these up you get the $213