Answer: 5% interest rate
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Work Shown:
The given values are
A = 5205.75
P = 3500
n = 4
t = 8
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Plug those values in. Isolate r.
A = P*(1+r/n)^(n*t)
5205.75 = 3500*(1+r/4)^(4*8)
5205.75 = 3500*(1+r/4)^(32)
3500*(1+r/4)^(32) = 5205.75
(1+r/4)^(32) = 5205.75/3500
(1+r/4)^(32) = 1.48735714285714
1+r/4 = (1.48735714285714)^(1/32)
1+r/4 = 1.01248355256014
r/4 = 1.01248355256014-1
r/4 = 0.01248355256014
r = 4*0.01248355256014
r = 0.04993421024056
r = 0.0499
Multiply this r value by 100 to convert to a percentage
100*r = 100*0.0499
100*r = 4.99%
Rounding to the nearest tenth, we get 5.0% or just 5%
and 
, the product is
and 
, so the product is
