Subtraction and find missing numbers quiz online. Children will learn to balance subtraction equations by finding the missing numbers which complete the equation. This topic is in line with pre-algebra that children will study in higher levels. However, the numbers are small at this level to make it easy for beginners. Fill in the missing number and improve your subtraction skills. This subtraction exercise if for kids in 1st, 2nd, 3rd, and 4th grades