1. Find A's cost price:
Let A's cost price be 'x'.
A sells to B at 25% profit, so B's cost price is 125% of A's cost price.
125% of x = Rs. 300
(125/100) * x = 300
x = (300 * 100) / 125 = Rs. 240
2. Find B's selling price (which is C's cost price):
B sells to C at a 10% loss, so C's cost price is 90% of B's cost price.
C's cost price = 90% of Rs. 300 = (90/100) * 300 = Rs. 270
3. Calculate the percentage of C's cost price to A's cost price:
Therefore, C's cost price is equal to 112.5% of A's cost price.