SOLUTION: for a given interest rate, simple interest varies jointly as the principal and time. If $3000 left in an account for 4 years earned interest of $960 then how much interest would be

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Question 1019207: for a given interest rate, simple interest varies jointly as the principal and time. If $3000 left in an account for 4 years earned interest of $960 then how much interest would be earned in 7 years
Answer by robertb(5830) About Me  (Show Source):
You can put this solution on YOUR website!
The simple interest formula is I = Prt.
Now here, P = 3000, t = 4, and I = 960. Substituting these values into the formula, we get
960 = 3000*r*4
==> r = 2/25,or in percent, 8%.
Thus, the interest earned after 7 years would be
I = 3000*0.08*7 = $1,680.