Subtract by counting back

Day 1 Teaching
Ask children how we could solve 65 – 24. Do we count back in ones? Draw out that we can count back 20, and then subtract 4. Say we use a number fact: 5 – 4. Repeat for 85 – 24. Draw on the landmarked line, and also as an empty number line jotting. Repeat for 85 – 30, 85 – 33, 77 – 33, 96 – 32.
Group Activities
-- Play a card game to subtract two 2-digit numbers and draw accurate empty number lines.
-- Subtract two 2-digit numbers: identify answers that will be less than 50.

Day 2 Teaching
Show 85p as 50p, three 10ps and a 5p coin. A banana is 33p. Move away three 10p coins and count back in 10s. Now we take away 3. What is 5 take away 3? Remove the 5p coin and replace with a 2p coin. Repeat with similar subtractions.
Group Activities
Use the in-depth problem-solving investigation ‘Build it Up’ from NRICH as today’s group activity.
Or, use this activity:
-- Find missing numbers in subtraction calculations.

• 0 to 100 landmarked line (see resources)
• Red and yellow cards to write on
• Beads
• ‘Subtracting 2-digit numbers by counting back on a beadstring’ sheets (see resources)
• 0 to 100 beaded lines (see resources)
• Blank cards to write on
• Cubes
• Coins – real and for display on the IWB
• Sticky notes

Day 1
Using subtraction facts (pre-requisite skills)

Day 2
Using addition and subtraction facts (pre-requisite skills)

Day 1
Subtract pairs of 2-digit numbers, recording jottings on beaded, landmarked or empty number lines.

Day 2
Solve and create subtraction word problems.

• Write the steps in this subtraction to help Zoe.
  56 – 34
  Count back in tens.
  56 ___ ____ ____
  Subtract 4 ____
  56 – 34 = ____
• Mia has 69p, Tom has 88p and Padma has 37p.
  Each child spends 34p.
  How much does each have left?
• Explain how you would subtract 55p from 98p.
  Complete this subtraction grid

• Mark Jo’s homework. Write the correct answers.
  75 - 23 = 98
  86 - 32 = 55
  67 - 24 = 43
  64 - 42 = 20
  

In-depth Investigation: Built it Up
Can children find all the ways to get 15 at the top of a triangle of numbers? A good opportunity to explore the relationship between addition and subtraction. Build it Up from nrich.maths.org.

Spot the Pattern
Using number facts and patterns to subtract 1-digit numbers from 2-digit numbers, e.g. 6 - 3, 16 - 3, 26 - 3, 36 - 3... 96 - 3