Three maths classes: X, Y and Z take an algebra test. The average score of class X is 83. The average score of class Y is 76. The average score of class Z is 85. The average score of class X and Y is 79 and average score of class Y and Z is 81. What is the average score of classes X, Y, Z?	Options:
A) 81.5
B) 80.5
C) 83
D) 78
E) 87
Let the number of students in classes X, Y and Z be A, B and C respectively.   Then, total score of X= 83A, total score of Y = 76B, total score of Z = 85C.   Also given that,   (83A + 76B) / (A + B) = 79   =&gt;4A = 3B.   (76B + 85C)/(B + C) = 81   =&gt;4C = 5B,   =&gt;B = 4A/3 and C = 5A/3   Therefore, average score of X, Y, Z = ( 83A + 76B + 85C ) / (A + B + C) = 978/12 = 81.5.   81.5NSWER:81.5
<result>A</result>
Three maths classes: X, Y and Z take an algebra test. The average score of class X is 83. The average score of class Y is 76. The average score of class Z is 85. The average score of class X and Y is 79 and average score of class Y and Z is 81. What is the average score of classes X, Y, Z?