On a certain sum, C.I. is Rs 41 and SI is Rs 40. for 2 years. What is the rate p.a.

I noticed you posted this same question three times.

I don't recognize C.I. and SI
Please define them.

CI = compound interest

SI = simple interest

To find the rate of interest per annum (p.a.), you can use the formula:

Rate = (Simple Interest/Principal) x (100/Time)

In this case, the principal is the amount of the sum, the simple interest is Rs 40, and the time is 2 years.

First, let's find the principal amount:

Principal = Simple Interest + Compound Interest
Principal = Rs 40 + Rs 41
Principal = Rs 81

Now, we can calculate the rate:

Rate = (Simple Interest/Principal) x (100/Time)
Rate = (Rs 40/Rs 81) x (100/2)
Rate = (40/81) x 50
Rate = 0.4938 x 50
Rate ≈ 24.69%

Therefore, the rate per annum is approximately 24.69%.