compound interest

[bunnyne]

Sam invests a sum of money into an account that pays 3% compound interest per annum.
Work out after how many years Sam will have doubled his investment.
Give your answer as a whole number of years.

I wasn't sure about this question. I've been doing compound interest recently and have understood it perfectly. I have a great teacher, but ended up stuck on the last question.

 

[Deleted member 4993]

Sam invests a sum of money into an account that pays 3% compound interest per annum.
Work out after how many years Sam will have doubled his investment.
Give your answer as a whole number of years.

I wasn't sure about this question. I've been doing compound interest recently and have understood it perfectly. I have a great teacher, but ended up stuck on the last question.

Please tell us the formula for compound interest.

 

[bunnyne]

starting amount x (multiplier)^n

 

[JeffM]

If you cannot solve a general question, think about solving a specific question.

Question 1: Could you figure out how many years it would take for $1,000 to increase to at least $2,000 if the money is invested at 3% per annum? How would you do that?

Question 2: Have you ever heard of an exponential equation? Do you know how to solve that type of equation?

 

[Deleted member 4993]

starting amount x (multiplier)^n

That is not incomplete.

The equation (formula) for simple interest would be:

A = P * r * t + P .....................................where

P = starting amount

t = time it is earning interest

r = rate of Interest during time 't'

A = Amount collected at the end of time period 't'

What is the equivalent equation for "compound" interest?

Please define all the variables in the equation (like I defined P, t, r & A)