In a class, there are 'z' students. Out of them 'x' are boys. What part of the class is composed of girls ?

Answer: Option C

Total students = z
Total boys = x
Total girls = z - x
⇒ $$\frac{\text{Number of girls}}{\text{Total students}}$$
= $$\frac{z-x}{z}$$
= 1 - $$\frac{x}{z}$$