Question

the numbers of girls in the choir is 4 times the number of boys in the choir .the total number of students is 60..how many girls?

Answer 1

First, make up some variables to represent the number of Girls and Boys in the choir.  

B = number of boys
G = number of girls

You know that there are 4 times as many girls in the choir as boys.  Therefore, the equation you can write is:
$\frac{B}{G} = \frac{1}{4}$

If you cross-multiply, then you get the simplified equation:
G = 4B

Intuitively this makes sense since if you multiplied the number of boys in the class by 4, that would be equal to the number of girls you have.

Now, we know that the total class size is 60. So girls plus boys equals 60:
G+B = 60

To solve the equation, replace the G in this equation with the replacement you found before, 4B.
G + B = 60 -->
4B + B = 60 -->
5B = 60 -->
B = 12

However, you are trying to find the number of girls, so plug the answer back into your equation.
G + B = 60 -->
G + 12 = 60 -->
G + 12 -12 = 60 - 12 -->
G = 48

The number of girls you have is 48.