Question

Diego deposits $4,200 into a savings account that pays 5% simple interest. He decides not to touch the money until it doubles. How long will Diego have to keep the money in this account?

Answer 1

Principal money deposited by Diego into the savings account = $4200
Final amount of money taht Diego will get = (4200 * 2) dollars
                                                                   = 8400 dollars
Percentage of simple interest given = 5%
Let us assume that after x years the money is going to double.
Then
Amount = Principal (1 + rate of Interest * Time)
8400 = 4200[ 1 + (5/100) * x]
8400/4200 = 1 + (x/20)
2 = 1 + (x/20)
2 - 1 = x/20
x/20 = 1
x = 20
So after 20 years the money will get doubled.