Question

13. The average weight of all the students of classes I and II
equals the average of the average weight of the students
of the two classes. There are twice as many students
in class II as in class I. The sum of twice the average
weight of the students of class I and the average weight
of the students of class II is 60 kg. Find the average
weight of class I (in kg).
(A) 10 (B) 15
(C) 20
(D) 25​

Answer 1

Given :- The average weight of all the students of classes I and II equals the average of the average weight of the students of the two classes. There are twice as many students in class II as in class I. The sum of twice the average weight of the students of class I and the average weight of the students of class II is 60 kg. Find the average

weight of class I (in kg).

(A) 10

(B) 15

(C) 20

(D) 25

Answer :-

Let us assume that,

• Total students in class I = x
• Total students in class II = 2x
• Average weight of class I = A
• Average weight of class II = B

so,

→ A*x + B*2x/(x + 2x) = (A + B)/2

→ 2Ax + 4Bx = 3Ax + 3Bx

→ 4Bx - 3Bx = 3Ax - 2Ax

→ Bx = Ax

→ A = B ------ Eqn.(1)

also, given that,

→ 2A + B = 60

putting value of Eqn.(1)

→ 2A + A = 60

→ 3A = 60

→ A = 20 kg (C) (Ans.)

Hence, the average weight of class I is 20 kg.

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