Question

30 girls and boys have planed for picnic.there is ratio of 3 girls to 7 boys how many boys are there? 

Answer 1

total students = 60
so we have 3 girls for 7 boys 
so no of girls = 3x
no of boys = 7x

so total students 3x + 7x = 60
                           10x = 60
                              x= 6

no of boys = 7 x 6 = 42

Answer 2

given
ratio of girls and boys are=3:7
ratio of boys is =7x
ratio of girls is =3x
total=60
sum of ratio of boys and girls =total
 7x+3x=60
10x=60
x=6
 sub x in ratio of boys
boys=7x
7(6)
42 is answers