Calculate complements to 100 (4)

Only premium members can download this resource. You can sign up for a membership here.

Description

Calculating complements to 100 is an important skill, because it is a prerequisite for calculating how much change is due when paying for an item. When pupils calculate complements (the amount needed to complete a total), a common error is to end up with a total that is too large:

  • When calculating complements to 100, pupils typically make an extra ‘unit’ of 10, making 110 instead of 100.
  • When finding change from a whole number of pounds, pupils typically make an extra £1, for example, they incorrectly calculate the change due from £5 for a cost of £3.40 as £2.60.

It is important for pupils to spend time specifically learning about calculating complements, including the risk of creating ‘extra units’. This should begin in year 3, with calculating complements to 100.

Pupils should compare correct calculations with the corresponding common incorrect calculations for complements to 100. They should be able to discuss the pairs of calculations and understand the source of the error in the incorrect calculations.

A shaded 100 grid can be used to show why there are only 9 full tens in the correct  complements to 100. The 10th ten is composed of the ones digits.

Once pupils understand why given complements to 100 are correct or not, they should learn to work in steps to calculate complements themselves:  1. First make 10 ones.  2. Then work out the number of additional tens needed. Pupils must understand that the tens digits should bond to 9, not to 10. 3. Check that the 2 numbers sum to 100.

Language focus “First we make 10 ones. The ones digits add up to 1 ten, so we need 9 more tens.”

Additional information

Objectives

Reviews

There are no reviews yet.

Be the first to review “Calculate complements to 100 (4)”

Your email address will not be published.

Love Our Lesson Plans?

Get more teaching tips and worksheets by signing up to our mailing list.

Our Blog

a teacher planning student progression
A Guide to White Rose Maths Small Steps Progression Planning

White Rose Maths is an organisation that provides maths resources and lesson planning materials to help teachers adopt a maths mastery approach. Their mission is to support teachers in improving maths education and prove that, with the right support, all children can do maths. They offer Schemes of Learning that break down what children should…

Only premium members can view this post. You can sign up for a membership here.

Read More
Primary students doing maths activities on a white board
Teaching White Rose Maths Mastery to Primary Pupils

White Rose Maths is an organisation that has become a thought leader in the world of maths education. They’ve changed how teachers approach maths lessons and helped children all around the UK adopt a positive, growth mindset when tackling number problems and maths concepts. The White Rose Maths motto is “Everyone Can Do Maths: Everyone…

Only premium members can view this post. You can sign up for a membership here.

Read More
child completing a white rose maths worksheet
White Rose Maths Resources: Enhance Children’s Learning Experience

White Rose Maths is an organisation that’s been helping schools in the UK to improve maths education and instil a love of learning in children for several years. They provide maths resources and Schemes of Learning to help children progress through the National Curriculum in small steps and develop confidence and competence in mathematics. The…

Only premium members can view this post. You can sign up for a membership here.

Read More
Menu