Discussion of Question with ID = 002 under Alligations-and-Mixtures

This is the discussion forum for this question. If you find any mistakes in the solution, or if you have a better solution, then this is the right place to discuss. A healthy discussion helps all of us, so you are requested to be polite and soft, even if you disagree with the views of others. The question and its current solution has also been given on this page.

Advertisement

Question

The average weight of the students of a class is 4 Kg, and the average weight of the students of another class is 14 Kg. What is the ratio of the number of students in the two classes if the combined average weight is 13 Kg?

A

${1/9}$.

B

$1{1/4}$.

C

$1{8/11}$.

D

$2{6/11}$.

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). So the ratio is ${A_2 - A}/{A - A_1 }$. Putting A2 = 14, A1 = 4, and A = 13, we have ${14 - 13}/{13 - 4 }$, from where we get the ratio as ${1/9}$.

Comments and Discussion