Answer : Option C

Explanation :

ATQ, the difference between profit % = 5
The difference between S.P = 10

Apply formula:

C.P = (100* Difference between S.P)/ (% difference in profit)

Hence, the C.P = (100 * 10)/ 5 = 200.

The difference between profit = 5%
Let the C.P = x
And S.P2= 1010, S.P1 = 1000

i.e., P2 % - P1% = 5.................................................... (i)

Apply formula of percent

P% = (Profit/C.P) * 100

And profit = S.P - C.P.

Now according to equation (i)

((S.P 2- x)/ x)*100 - ((S.P 1- x)/ x)*100 = 5

((1010- x)/ x)*100 - ((1000- x)/ x)*100 = 5

Or, take (100/x) as common from the whole equation.

i.e., (100/x) [(1010-x) - (1000-x)] = 5

(100/x) [1010 - x - 1000 + x] = 5

Or, (100/x) * 10 = 5

Or, 5x = 1000
Hence, x = 200, or C.P = Rs 200.