Question

14. In a class of 56 students, number of boys is 2 more
than number of girls. The average weight of boys is
50 kg and average weight of the class is 45 kg. Find
the average weight of girls.
(a) 39.6
(b) 39.5
(c) 39.33
(d) 39.25​

Answer 1

Answer:

Let the number of girls x , number of boys will be x+2 . Total students in class will be 2x + 2 .

Given that

$2x + 2 = 56 \\ 2x = 54 \\ x = 27$

Now Average weight of a boy is 50 kg so total weight of x+2 boys will be 50(x + 2) .

Similarly total weight of class will be 45(2x + 2)

27 Girls weight will be

= Weight of total class - boys

$= 45(2x + 2) - 50(x + 2) \\ = 90x + 90 - 50x - 100 \\ = 40x - 10 \\ = 40 \times 27 - 10 \\ = 1070 \: kg$

So average

$= \frac{1070}{27} \approx \: \frac{ \cancel{1071} {}^{119} }{ \cancel{27 }{ {}^{3} }} = 39.6 \: kg$