SOLUTION: I need help setting up an equation and solving it. Can you please help me? Sal has $3200 invested in an account paying 7.2% interest per year. At what rate must he invest an a

Question 561720: I need help setting up an equation and solving it. Can you please help me?
Sal has $3200 invested in an account paying 7.2% interest per year. At what rate must he invest an additional $2800 so that the annual interest from the two investments will be $390?
I have to use the formula p*r*t=I
Can you please help me set up the equation and help solve it?
Answer by ankor@dixie-net.com(22740) (Show Source): You can put this solution on YOUR website!
Sal has $3200 invested in an account paying 7.2% interest per year.
At what rate must he invest an additional $2800 so that the annual interest from the two investments will be $390?
:
Let r = rate required for the $2800 to get a total $390 return
I = P*r*t
where
p = 2800
r = interest rate
t = 1 yr
:
.072(3200) + (2800*r*1) = 390
230.40 + 2800r = 390
2800r = 390 - 230.40
2800r = 159.60
r =
r = .057 ~ 5.7% is the rate required
:
:
Check this
.072(3200) = 230.40
.057(2800) = 159.60
---------------------
total int: = 390.00

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