Question

The mean weight of the students in a certain class is 60 kg. The mean weight of the boys from the class is 70 kg and that of the girls is 55 kg. What is the ratio of the number of boys to that of girls? 

(a) 2 : 1 

(b) 1 : 2 

(c) 1 : 4 

(d) 4 : 1

Answer 1

(b) 1 : 2

Let the number of boys be x and the number of girls be y.

Then, \(\frac{70\times{x}+55\times{y}}{(x+y)}=60\)

⇒ 70x + 55 y = 60x + 60y 

⇒ 10x = 5 y ⇒ \(\frac{x}{y}=\frac{5}{10} = \frac{1}{2}\) ⇒ x : y = 1 : 2.