How long would it take for the value of the per year interest quadruple?

Question

A principal earns 5% per year simple interest. How long will it take for the future value to quadruple? (Round your answer to two decimal places.)

What would the formula be to find the answer to this question? Would it be include $$(.05)\times (1)$$

Answer 1

Here is the formula with y=number of years $$1+0.05y=4$$

A better way to look at this is to note that quadrupling is equivalent to increasing by 300%, and because this is simple interest, we can simply divide 300 by 5.