AILET 2015 Question Paper with answer key for online practice

Three maths classes: X, Y and Z take an algebra test. The average score o* 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 and Z ?