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Parviz F. | Mathematics professor at Community CollegesMathematics professor at Community Colle...

In a Simple interest rate, where Money grows at fixed rate each year is given a linear equation, because rate of change is fixed ( throughout the year). A is the balance of the account after n( variable) years with a fixed rate( slope).

A = P + Pnr / here the n is the variable.

7800 = P( 1 +3(0.05)=

7800 = P + P( 0.15)

P = 7800 = 6783

1.15

i=p*r*t

A=p+i

A=p+p*5%*3

$7820=p+p*0.05*3

$7820=p+p*0.15

$7820=(1+0.15)*p

$7820=1.15*p

$7820/1.15=p

$6800=p, the principal or how much was borrowed

check: i=$6800*0.05*3

i=$6800*0.15

i=$1020

A=$6800+$1020=$7820

Hi Noah;

By definition, SIMPLE INTEREST means that there is no compounded interest.

I am assuming that the 5% rate is per year.

$7820=(principal)+[(principal)(rate)(time)]

$7820=(principal)+[(principal)(rate)(time)]

$7820=(principal)+[(principal)(0.05/year)(3 years)]

The unit of year is in the numerator and denominator. It cancels.

$7820=(principal)+[(principal)(0.05/year)(3 years)]

$7820=(principal)+[(0.15)(principal)]

$7820=(1.15)(principal)

Let's divide both sides by 1.15...

$6800=principal

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