The ratio is a way of comparing or expressing a relation between two quantities which is measured in same unit. If the ratio of two numbers is 4:1, then we can say that the first number is four times larger than the second number. For example, principle can look in the college, and refer as "ratio of female teacher to male teacher" in a school. If a school has 80 female teacher and 20 male teacher, then the ratio of female and male teacher is 80 to 20. We can also say that the ratio of female teacher to male teacher is 4 to 1.
A ratio is a comparison between two numbers and it is described as a fraction. If x and y are any two numbers, then the ratio of x to y is $\frac{x}{y}$ , $(y \neq 0)$.
To simplify the ratio we can make the numbers into smaller ratios so as to compare easily. This can be done by dividing the ratio by same number on each side.

Example: The ratio of girl to boy in a class is 12:16.
 Calculating RatioRatio Calculation
Dividing 2 on both 12 and 16 as 2 is the common factor: 

      $\frac{12}{2}$ = $6$

      $\frac{16}{2}$ = $8$

So, 12 : 16 is simplified into 6 : 8.

 Ratio CalculatorHow to Calculate Ratio
To see this ratio into simpler way,again divide both 6 and 8 by 2:

       $\frac{6}{2}$ = $3$

       $\frac{8}{2}$ = $4$

therefore, 6 : 8 is simplified into 3 : 4.

Hence, the ratio of girl to boy in a class is 3 : 4.