Three math classes X, Y, and Z take an algebra test. The average score in class X is The average score in class Y is The average score in class Z is The average score of all students in classes X and Y together The average score of all students in classes Y and Z together is What is the average for all the three classes?
Solution
Correct Answer: Option B
Let no of people in class X,Y,Z be x,y,z respectively, total x = 83x total y = 76y total z = 85z
total(x+y) = 79(x+y) total(y+z) = 81(y+z)
implies 83x + 76y = 79(x+y) --------1 76y + 85z = 81(y+z) --------2
1 is 3y=4x 2 is 5y=4z
average of 3 classes = total( x + y + z )/( x + y + z)
= (83x+76y+85z)/( x + y + z)
= 978/12
= 81.5
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