The average weight of all the students of a class is 55 Kg.  The ratio of the average weight of Boys and Girls is 5 : 4.  If 40% of the students are boys and rest are girls.  Find the average weight of boys.

62.5

Let the common ratio = R

ATQ,

⇒ \(\frac{5R\;- \;55}{55\;-\;4R}\) = \(\frac{3}{2}\)

⇒ 10R - 110 = 165 - 12R

⇒ 22R = 275

⇒ R = 12.5

⇒ Boys = 12.5 × 5 = 62.5