In this task, you need to answer the given multiple-choice question on the general math. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.

[Q]: Problem: a 20 litre mixture of milk and water contains milk and water in the ratio 3 : 2 . 10 litres of the mixture is removed and replaced with pure milk and the operation is repeated once more . at the end of the two removal and replacement , what is the ratio t of milk and water in the resultant mixture ? 
Options: a ) 17 : 3 , b ) 9 : 1 , c ) 3 : 17 , d ) 5 : 3 , e ) 11 : 2
[A]: b


[Q]: Problem: if a - b = 5 and a 2 + b 2 = 31 , find the value of ab . 
Options: a ) 9 , b ) 2 , c ) 3 , d ) 7 , e ) 12
[A]: c


[Q]: Problem: in a mixture 60 litres , the ratio of milk and water 2 : 1 . if this ratio is to be 1 : 2 , then the quanity of water to be further added is : 
Options: a ) 20 , b ) 30 , c ) 40 , d ) 50 , e ) 60
[A]:
e