### Teaching and Group Activities for Understanding

**Day 1 Teaching**

Children list the pairs of factors of 20. Write 20 × 36 on the board. Agree that we can solve this by multiplying 36 by 2, then by 10 (or vice versa). Explain that when we do this we are using the factors of 20. Encourage children to reflect on their preferences: Which way did you find quicker or made more sense? Children list the pairs of factors for 14, then use factors to work out 14 × 52. Repeat for 24 × 45.

**Group Activities**

Use the ‘Race to 200’ in-depth problem-solving investigation below as today’s group activity.

Or, use these activities:

-- Children multiply 23 by 8, 12, 14, 16 and 18 by listing factors and using a chosen pair to aid multiplication.

-- Use a ‘broken’ calculator to multiply 379 by 6, 8, 12, 18 and 24 by listing factors and using a chosen pair to aid multiplication.

**Day 2 Teaching**

Write 2 + 7 + 8 and ask children how they would work this out. Draw out changing the order to add the pair to 10, then add 7. Say that multiplication can also be done in any order. Write 4 × 7 × 5. How could we change the order of this multiplication that might simplify the calculation? Model reordering as 4 × 5 × 7, i.e. working out 20 × 7. Repeat with 7 × 2 × 8.**Group Activities**

-- Children multiply three numbers 2-9, recognising where reordering can simplify the calculation. Record the multiplication in order in books; write a sentence to explain choice.

-- Children multiply three numbers, recognising where factors and reordering can simplify the calculation. Record the multiplication in order in books; write a sentence to explain choice.