Question

The average weight of 120 students in the second year class of college is 56 kg. If the average weight of boys and that of girls in the class are 60 kg and 50 kg respectively, then find the number of boys and girls
in the class.
(a) 72,62
(b) 38,64
(c ) 72,48
(d) 62,58

Answer 1

Hint: Sum of weight of all boys will be the total number of boys multiplied by their average weight. Similarly we can find the sum of weight of all girls.

Complete step-by-step answer:
Given, the average weight of 120 students in the second year class of college is 56 kg and the average weight of boys and that of girls in the class are 60 kg and 50 kg respectively.

Let us take the number of boys as x.
Then, we can find the number of girls = (total number of students- number of boys)= (120 - x)
Now find the total weight of 120 students in the class = $120 \times 56 kg$
By multiplying we get, the total weight of 120 students as 6720 kg
As the average weight of boys is 60 thus the total weight of x boys = 60x kg
As the average weight of boys is 50 thus the total weight of (120 - x) girls = 50(120 - x) kg = 6000 - 50x
Equating the total weight of 120 students and the sum of total weight of x boys and total weight of (120-x) girls
Thus, 60x + 6000 - 50x = 6720
By solving the equation we get,
10x = 720
Find x from the equation,
 x = 72
Thus the number of boys = 72,
Number of girls = 120 - 72 = 48

Note: In such a type of question we can take the number of boys as x and then proceed to find the equation.