Question

the number of boys and girls in a class are in ratio7:5the the number of boys and girls in a class are in the ratio 7 is to 5 the number of boys is 8 more than the number of girls what is the total class strength

Answer 1

Let
Boys = b
Girls = g 


The number of boys and girls in a class are in the ratio 7:5
b:g=7:5
b/g=7/5
b5=g7
b5/5=g7/5
b=g7/5...............(1) 
the number of boys is 8 more than the number of girls


b=g+8.............(2)
Put the value of b from (1) to (2)
g7/5=g+8
5*(g7/5)=5*(g+8)
g7=5g+40
g7-g5=40
2g=40
2g/2=40/2
g=20
Put the value of g in (2)
b=20+8
b=28 
Boys are 28 and Girls are 20
Therefore total number of students is 48

Answer 2

Let the no. of girls be 5x
No. of boys=7x
According to the question
5x+8=7x
7x-5x=8
2x=8
x=8/2
x=4
No. of girls=5*4=20
no. of boys=7*4 or 5*4+8=28
Hence the total strength of the class is 20+28=48

Hope it helps u.