Discussion of Question with ID = 037 under Alligations-and-Mixtures

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Question

The average weight of a class of 30 students is 13 Kg, and the average weight of a class of 60 students is 7 Kg. What is the average weight of the two combined classes?

A

9 Kg.

B

10 Kg.

C

8 Kg.

D

12 Kg.

Soln.
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 = 30, A1 = 13, n2 = 60 and A2 = 7, we get A = 9 Kg.


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