Composition of numbers: 11–19

Introduction

Explore the ten-and-a-bit nature of the numbers 11–19, using the partitioning structure; apply number facts within ten to addition and subtraction of single-digit numbers to/from the numbers 11–19.

Teaching points

• Teaching point 1: The digits in the numbers 11–19 tell us about their value.
   
• Teaching point 2: The numbers 11–19 can be formed by combining a ten and ones, and can be partitioned into a ten and ones.
   
• Teaching point 3: A number is even if the ones digit is even; it can be made from groups of two. A number is odd if the ones digit is odd; it can’t be made from groups of two.
   
• Teaching point 4: Doubling the numbers 6–9 (inclusive) gives an even teen number; halving an even teen number gives a number from six to nine (inclusive).
   
• Teaching point 5: Addition and subtraction facts within 10 can be applied to addition and subtraction within 20.