A sum of Tk. 312 was divided among 100 boys and girls in such a way that each boy gets  Tk. 60 and each girl Tk. 40, the number of girls is : 

Let x be the number of boys and y be the number of girls.  Given total number of boys and girls = 100 x+y=100           -------------- (i)

A boy gets Taka 3.60 and a girl gets Taka 2.40 The amount given to 100 boys and girls = Taka 312 3.60x+2.40y=312 -------------- (ii)

Solving (i) and (ii) 3.60x+3.60y=360       ------- Multiply (i) by 3.60 ⇒ 3.60x+2.40y=312 --------- (ii) 1.20y=48

y = 40