At what rate of CI per annum will be a sum of Rs. 1000 becomes Rs. 1040.4 in 2 years?

To find the rate of compound interest per annum, we can use the formula for compound interest which is:

A = P (1 + r/n)^(nt)

Where: A = the amount of money accumulated after n years, including interest. P = principal amount (the initial amount of money) r = annual interest rate (in decimal) n = number of times that interest is compounded per year t = time the money is invested for in years

Given in the problem: A = Rs. 1040.4 P = Rs. 1000 t = 2 years n = 1 (since it is compounded annually)

We can substitute the given values into the formula and solve for r:

1040.4 = 1000 (1 + r/1)^(1*2)

Divide both sides by 1000:

1.0404 = (1 + r)^2

Take the square root of both sides:

1.0201 = 1 + r

Subtract 1 from both sides:

0.0201 = r

To express the rate as a percentage, multiply by 100:

r = 0.0201 * 100 = 2.01%

So, the rate of compound interest per annum is approximately 2.01%.