Start by subtracting 0.9 from numbers and then move on to adding or subtracting 1.9, 2.9 using the same technique.

Using knowledge of the relationship between addition and subtraction, but in some of these questions, you need to adjust the numbers a little to give you the correct answers.

Work out mentally the answers to these sets of subtraction sums. For some, write down the method used to do it.

Plenty of practice subtracting tens of millions mentally.