Problems involving subtraction are more complex for children to handle than those involving addition. This is because they have to identify which quantity has to be taken away from which. This is very important because so far they were exposed to addition, where 2 + 3 = 3 + 2. But 9 - 3 is not the same as 3 - 9, that is, subtraction is, not commutative.

Let us now consider the different types of word problems related to subtraction that children come across. Broadly, there are four such models, namely:

• Complementary addition- What number/how many things should be added to one number or group to get the other. (e.g. "A crate can have 50 bottles. 20 bottles are already in it. How many more bottles can be put into the crate?")
  • It also helps children learn to subtract mentally and get comfortable with adding tens and ones in their heads. 
• Partitioning- An action of taking away or removing some objects, and finding out how many remain. (e.g., there were 15 toffees in this container, and 10 have been eaten. How many are left?)
• Reduction- When the original amount and the balance or remainder are known, to find the part that has been given away. (e.g., there were 15 toffees in a container, and there are only 5 now. How many have been eaten?)
• Comparison- The difference between two groups or numbers, namely, how much one is greater than the other, how much more is in one group than in the other. (e.g., if Munna has 15 erasers and Munni 5, how many less does Munni have than Munna?)

Hence, it can be concluded that the above problem is about complementary addition.