By selling an article at Rs.800, a profit of 25% is made. Find its cost price?	Choose the correct choice from the following answers:
A) s . 486 B) s . 455 C) s . 640 D) s . 480 E) s . 489

Rationale: sp = 800 cp = ( sp ) * [ 100 / ( 100 + p ) ] = 800 * [ 100 / ( 100 + 25 ) ] = 800 * [ 100 / 125 ] = rs . 640 answer : c
Answer: C