The time required for a sum of money to amount to five times itself at 16% simple interest p.a. will be.?

To solve this problem, we need to use the formula for simple interest which is I = PRT/100, where I is the interest, P is the principal amount, R is the rate of interest, and T is the time.

In this case, we know that the sum of money amounts to five times itself. This means that the interest earned is four times the principal amount (since the principal amount plus four times the principal amount equals five times the principal amount).

So, we can set up the equation as follows:

4P = PRT/100

We know that R = 16 (the rate of interest is 16%), so we can substitute this into the equation:

4P = P * 16T/100

We can simplify this to:

4 = 16T/100

Then, solve for T:

T = 4 * 100 / 16

T = 25 years

So, it will take 25 years for a sum of money to amount to five times itself at 16% simple interest per annum.