Discussion of Question with ID = 013 under Alligations-and-Mixtures

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The average weight of a class of 80 students is 11 Kg, and the average weight of a class of 160 students is 11 Kg. What is the average weight of the two combined classes?


11 Kg.


12 Kg.


10 Kg.


14 Kg.

Ans: a

If a sample n1 has a weighted average of A1, and another sample n2 has a weighted average of A2, then the weighted average, A,of the combined samples is determined by the alligation formula as: n1(A - A1) = n2(A2 - A). Putting n1 = 80, A1 = 11, n2 = 160 and A2 = 11, we get A = 11 Kg.

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