The least number of complete years in which a sum of money will be more than doubled at 10% compound interest is ________.

Since the number is more than double, the total amount will be at least twice the number.

If the number is x, the amount will be more than 2x.

Thus, $$2x\ge\ x\left(1+\frac{1}{10}\right)^{^r}$$

$$\left(1+\frac{1}{10}\right)^{^{r\ }}\ge\ 2$$

For r = 8, the value of $$\left(1.1\right)^r=2.143$$

Thus, the value of r will be 8.

Thus, the correct option is B.

Alternative:

No. of years in which a sum of money invested at r% compounded annually amounts to double is 72/r years

So, no. of years in which the amount will be doubled = 72/10 = 7.2 years

So, the least no. of years for which the amount will be more than doubled will be 8 years.