Question

30 girls and boys have planned for a picnic. There is a ratio of 3 girls to 7 boys. How many boys are there?

Answer 1

Let the common multiple be x.
Therefore, there are 3x girls and 7x boys.
Now,
According to question, there are 30 students in total
Therefore
3x+7x=30
10x=30
x=30/10
x=3

Now,
No. of girls = 3x = 3×3 = 9
No. o boys = 7x = 7×3 = 21

Hence 9 girls and 21 boys went to the picnic

Answer 2

let the no. of girls be 3x and boys be 7x,
so,a/q,
7x+3x=30
⇒10x=30
⇒x=3

hence, number of boys=21
and number of girls=9