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.

60 62.5 66 60.4

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