Mental addition means to add numbers in your head without writing down any steps or notes as part of the calculation. All of the calculations are done in your head.
There are various strategies for mental addition, however, with each method, it is important to hold values in your head. The fewer the steps, the better the methods as it is easier to hold the numbers in your head.
Pupils will start learning how to add numbers in their primary school. They'll practice applying their increasing knowledge of mental methods to solve addition problems. They'll continue to expand their knowledge by learning about more mental addition methods.