Verifying compound interest calculation with exponential formula

[alexandria]

Homework Statement

Homework Equations

A = P(1+i)^n

The Attempt at a Solution

Here is my attempted solution, can someone please verify if my method is correct!
Thanks in advance![/B]

 

[Ray Vickson]

Homework Statement

View attachment 101167

Homework Equations

A = P(1+i)^n

The Attempt at a Solution

Here is my attempted solution, can someone please verify if my method is correct!
Thanks in advance![/B]
View attachment 101166

It looks OK.

 

[phyzguy]

This is a good example of the "rule of 72", which is a rule of thumb used by financial people. Basically it says that the number of years it takes for an investment to double is equal to 72 divided by the annual percentage rate. In this case 72/4 = 18, quite close to your more exact solution.

 

[alexandria]

ok thanks for the help!