After 5 years, the simple interest earned on an investment of $3000 was $645. Find the interest rate.

The simple interest formula is:

A=P (1+rt)

P is the principle amount so P = $3000

A is the total amount accumulated

r is the rate divided by 100

t is the time

When t = 5, A = 3 645

so,

3 645 = 3000 (1+5r) - divide both sides by 3 000

1.215 = 1+5r - subtract 1 from both sides

0.215 = 5r - divide both sides by 5

0.043 = r

however, need to multiply r by 100 because the equation for r is R/100

so 0.43 x 100 is 4.3

The interest rate is 4.3% per year