Question: a can contains a mixture of liquids a and b is the ratio 7 : 5 . when 9 litres of mixture are drawn off and the can is filled with b , the ratio of a and b becomes 7 : 9 . how many liter of liquid a was contained by the can initially ?
A) 10
B) 20
C) 21
D) 25
E) 27
Correct answer: c
Grade: 6 | Topic: Ratios and proportions | Difficulty: Hard | Standard: 6.RP.A.3