Taking 15, 16, 17 or 18 from 2-digit numbers. The easiest way of doing this is by taking a whole ten and adjusting.

Use knowledge to subtract a single digit from a teen number quickly and efficiently. Rather than just counting up in ones, look for two steps, firstly to ten and then to the number.

More on the inverse relationship between addition and subtraction.

A look at the inverse relationship between addition and subtraction.