exchange

Changing a number or expression for another number or expression of equal value, is known as exchange.

We usually exchange currency to go abroad. For example, exchange pounds for dollars.

The exchange process is used in some concise standard calculation methods.

For example, carrying numbers in an addition sum, multiplication sum and division sum, and a subtraction by decomposition sum.

We also exchange in a mental arithmetic context.

For example:

   182 – 26
= 182 – 30 + 4
= 152 + 4
= 156