# Subtracting mentally in Year 3

Subtracting mentally in Year 3

Mental arithmetic should still be a vital part of lessons for children in Year 3 and we have just published three new sets of worksheets on specific skills of subtraction. The first set takes a look at subtracting 9 from 3-digit numbers. Children should already be familiar with the idea of taking 10 and adding 1 as a quick and efficient way of doing this, but will have worked with 2-digit numbers in year 2.

The second set looks at subtracting multiples of 10 from 3-digit numbers. These are not quite as easy as they might sound, as almost all of them cross a hundreds boundary e.g. 409 – 20 being 389.

The third set is another example of the popular bar modelling technique, this time for writing four number facts taken from a bar model. Key to this is understanding that subtraction is the inverse of addition. It can be found in the Year 3 Reasoning/Problem Solving category.

There are plenty of skills children need to be taught in year 3 to do with mental subtraction, including re-inforcing skills learned in Year 2. A complete list should include:

• subtracting by adjusting (e.g. taking 19 from a number by subtracting 20 and adding 1)

• subtracting multiples of 10 from 3-digit numbers (e.g. 345 – 50 = )

• subtracting single digits from 3-digit numbers (e.g. 345 – 8 = )

• mentally subtracting any 2-digit numbers (e.g. 34 – 27)

• subtracting multiples of 100 (e.g. 2300 – 400 =)

• subtracting by counting on (e.g. work out 301 – 297 by counting on from 297)

• understand subtraction as the inverse of addition and answers from a subtraction can be checked by adding.

With these skills it is surprising how little written subtraction needs to be used in the real world, as most calculations can be done mentally.

Don’t forget that as well as our Subtraction category there are also plenty of subtracting activities in our Reasoning/Problem Solving category, including some new ‘bar modelling’ pages.