A reduction of 20% in the price of oil enables a house wife to obtain 4kgs more for Rs.600, what is the reduced price for kg?  Choose the correct choice from the following answers:
A) 20
B) 40
C) 36
D) 30
E) 35

Rationale: "600 * ( 20 / 100 ) = 120 - - - - 4 ? - - - - 1 = > rs . 30 answer : d"
Answer: D