Arithmetic 

 

Three mathematics classes X,Y and Z take an geometry test. The average of class X is 64, The average of class Y is 80 and the average score of class Z is 76 . The average score of class X and Y is 70 while the average score of class X and Z is 68. What is the ratio of number of students in the class X,Y and Z?

(A) 6:10:3
(B) 5:3:1
(C) 10:6:5
(D) 3:10:1

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