Question

Jacob invested $300 in a savings account and earned $81 in interest at the end of 9 years. What was the interest rate?

Answer 1

Formula for simple interest is: I = P*r*t
where P is the Principal ($300)
r is the interest rate in decimal (?)
t is the number of years invested (9)
and I is the interest earned ($81).

Substitute the values into the formula and solve for r.

Answer 2

The "r" you solve will be in decimal. Multiply it by 100 to express it as a percentage.

Answer 3

The answer is 3%

Answer 4

3% is the correct answer. :)

Answer 5

The formula for finding the rate is more complicated than what Ranga posted.
The formula is located here: http://1728.org/compint2.htm
The correct formula for solving the interest rate is:
log(1 + rate) = {log(total) -log(Principal)} / Years
log(1 + rate) = {log(381) - log(300)} / Years
log(1 + rate) = (2.5809249757 - 2.4771212547) / 9
log(1 + rate) = 0.103803721 / 9
log(1 + rate) = 0.0115337468
We must raise 10 to the power of 0.0115337468 to get the value of 1 + rate
1 + rate = 10^0.0115337468
1 + rate = 1.0269132247
rate = .0269132247
rate = 2.69132247 %

And here's a calculator for checking that answer:
http://1728.org/compint.htm

Answer 6

lol ... Ranga's post is correct for the level involved.