One of the easiest ways of subtracting nine from a number is to subtract ten and then add one. This is a simple mental arithmetic 'trick' which many children do not pick up on and is much quicker than counting back nine using fingers etc. Probably the only time this method is not the most efficient is when the 2-digit number already has a 9 in the units. Here we have four pages on subtracting 9 from 2-digit numbers and if your child has really grasped this idea they should be able to fly through a page in no time at all! Subtracting 9 from a 2-digit number