Question

half of the number of boys in a class went to football ground to play. one-fourth of the number of boys went to library, remaining 10 boys went on other work. find the no. of boys in that class.

Answer 1

let the no of boys in the class =x
half of the boys =x/2
one fourth of the boys =x/4
remaining boys =10
x/2+x/4+10=x
2x+x+40/4=x
3x+40/4=x
3x+40=4x
40=4x-3x
40=x
no of boys in the class =40

Answer 2

let the total no. of boys = x
then, the boys gone to ground =x/2
also the boys went to lib. = x/4
boys went to other work= 10 
acc. to ques. 
x/2 + x/4 + 10 = x 
by taking lcm, 
(2x +x +40) /4 = x
3x + 40 = 4x
40= 4x - 3x
40= x
 checking,,
put x = 40
40/2 + 40/4 + 10 = 40
20 +10 +10 = 40 
40 = 40
l.h.s. = r.h.s.
checked so total no. boys is 40.....