Question 887032
the simple interest formula is as follows:
f = p + i * n * p which can be simplified to:
f = p * (1 + i * n)
f is the future value
p is the present value or principal
i is the interest rate per time period
n is the number of time periods.


you are given that 9000 grows at 7% per year for n years and results in 12150.


substitute in the equation of f = p * (1 + i * n) to get:


12150 = 9000 * (1 + .07 * n)


divide both sides of this equation by 9000 to get:


12150 / 9000 = 1 + .07 * n


simplify this to get:


1.35 = 1 + .07 * n


subtract 1 from both sides of the equation to get:


1.35 - 1 = .07 * n


simlify to get:


.35 = .07 * n


divide both sides of the equation by .07 to get:


.35 / .07 =  n


solve for n to get:


n = 5


since you now know the value of n, you can substitute in the first equation as follows:


the main equation is still f = p * (1 + i * n)


f = 14400
n = 5
i = .04


equation becomes:


14400 = p * (1 + .04 * 5) which becomes:


14400 = p * (1.2)


divide both sides of this equation by 1.2 to get:


14400 / 1.2 = p


solve for p to get:


p = 12000


the sum that you are looking for is 12000.