A reduction of 20% in the price of salt enables a lady to obtain 10kgs more for Rs.400, find the original price per kg?  Choose the correct choice from the following choices.
A) s . 7 B) s . 9 C) s . 10 D) s . 11 E) s . 19

Rationale: 100 * ( 20 / 100 ) = 20 - - - 10 ? - - - 1 = > rs . 2 400 - - - 80 ? - - - 2 = > rs . 10 answer : c
Answer: C