A sells a camera to B at profit of 20% and B sells it to C at a profit of 25%. If C pays Rs 450, what price did A pay for the camera ?

Let cost price for A = Rs. 100.
SP for A = CP for B = 100 + 20% of 100 = 120.
SP for B = CP for C = 120 + 25% of 120 = 150.

Given,
CP for C = 450
So,
150 = 450
1 = 450/150
100 = (450 *100)/150 = Rs. 300.
CP for A = Rs. 300.