The prices of tea and coffee per kg were the same in june. In july the price of coffee shot up by 20% and that of tea dropped by 20%. if in july , a mixture containing equal quantities of tea and coffee costs 40/kg. how much did a kg of coffee cost in june ?  Choose the correct choice
A) 40
B) 60
C) 80
D) 100
E) 120

Rationale: "let the price of tea and coffee be x per kg in june . price of tea in july = 1.2 x price of coffee in july = 0.8 x . in july the price of 1 / 2 kg ( 400 gm ) of tea and 1 / 2 kg ( 400 gm ) of coffee ( equal quantities ) = 40 1.2 x ( 1 / 2 ) + 0.8 x ( 1 / 2 ) = 40 = > x = 40 thus proved . . . option a ."
Answer: A