In what ratio must water be mixed with milk to gain 16 2/3% on selling the mixture at cost price ?	Choose the correct choice from the following answers:	A) 1 : 9	B) 1 : 1	C) 1 : 2	D) 1 : 6	E) 1 : 5

Rationale: required ratio is cheaper quantity : dearer quantity = ( d - m ) : ( m - c ) answer with explanation : step i ) let c . p of 1 litre of mild be rs . 1 and s . p of 1 litre of mild be rs . 1 gain = 50 / 3 per cent  c . p of 1 litre of mixture =              1 3 50 100 100 x = re . 100 x 3 / 350 x 1 = 6 / 7 ( mean price ) step ( ii ) by the rule of allegation i . c . p of 1 liter of water = 0 ii . c . p of 1 liter of milk = 1 iii . mean price ( p ) = 6 / 7 iv . d – m = 1 – 6 / 7 = 1 / 7 v . m – c = 6 / 7 - 0 = 6 / 7  ratio of water and milk = 1 / 7 : 6 / 7 = 1 : 6 answer : d
Answer: D