algebra simple intrest

Question

The amount of simple interest, I , which is earned in an investment period is jointly proportional to the amount invested P and the time T of the investment period. If P = $400 and T = 2 years, then I = $40 . Find the amount of simple interest earned when $500 is invested for 1 year.

 

 

need help reall bad i cant find a solution anywhere

Answer 1

Hello JaNae,

 

We can say

 

I = kPT 

 

Where I, P and T are defined as above

k is a constant

 

Now let's plug in the values you have and solve for k

 

40 = k(400)(2)

40 = 800k

k = .05

 

Now let's restate the original equation with the calculated value of k

I = 0.05PT

 

And finally plug in the values in the last sentence of the problem and solve for I.

 

I = (.05)(500)(1)

I = $25