Problem Solving

Someone invested x dollars at simple annual interest, and the investment, including interest will be doubled in 8 and 1/3 years. What will be the total amount of the investment after 25 years?

OA given is 4X

I reckon the solution is as follows:

From the formula of SI,

Total amount = P + PRN/100

So, total amount at the end of 8 & 1/3 years will be: 2x = x + (x*r*100/12*100)[ 8 & 1/3 years = 100 months and 12 in the denominator because 12 months in a year]

Solving the equation we get, r = 12%.

Now, for total amount after 25 years,

Total amount = x + (x*12*25)/100.

Upon solving we get, total amount = 4x.

Hope this helps.

Thanks

2x = x + (x*r*n)/100