Math lesson plan · 5th grade (Year 6 in England) · 30 minutes
Mental multiplication tricks: ×5, ×25, ×9, ×99 and doubling and halving
Multiplication and division
CCSS 5.NBT.B.5England: Y6 Multiplication and division
Objective and success criteria
Students will: Mental multiplication tricks: ×5, ×25, ×9, ×99 and doubling and halving.
- I can answer questions on today's skill on my own, without help.
- I can explain each step and say why it works.
- I can check my answer and spot a mistake.
Before and after
Needs first: Multiply multiples of 10, 100 and 1000 mentally
Leads to: the next skill in this area.
Materials: Counters for arrays, Multiplication grid, Base-ten blocks, Mini whiteboards and pens, Printed student sheet (below).
Warm-up · 4 min
- Quick retrieval from earlier learning (Multiply multiples of 10, 100 and 1000 mentally). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- 30 × 60 = ? → 1800Prompt: Start with the basic fact 3 × 6.
- 60 × 500 = ? → 30000Prompt: 6 × 5 = 30. Careful: this fact already ends in a zero.
- Ravi needs 16 000 tiles. They come in boxes of 20. How many boxes does Ravi need? → 800Prompt: 20 × ? = 16 000
Hook · 3 min
- Show an array of chairs, eggs or windows and ask how many there are without counting one by one.
- Share the objective: Mental multiplication tricks: ×5, ×25, ×9, ×99 and doubling and halving. Read the success criteria together.
I do: model it · 7 min
- Work through the example out loud, saying why you do each step, not just what you do.
- Example: 38 × 5 = ?
- Step 1: 38 × 10 = 380, 380 ÷ 2 = 190
- Step 2: 38 × 5 = 190
- Answer: 190
- Pause after each step and ask a student to say what comes next.
We do: guided practice · 6 min
- Do these together. Students try each step on whiteboards before you reveal it.
- Use the hints as prompts rather than giving the answer.
- 39 × 99 = ? → 3861Prompt: × 99 is × 100 then take away one lot.
- Use doubling and halving to work out 26 × 45. → 1170Prompt: Halve 26 and double 45.
You do: independent practice · 7 min
- Students work on the student sheet. Circulate and check the first two answers of every student early.
- Students who finish: write a question of their own for a partner, with the answer.
The 6 questions are on the student sheet below, with answers in the key.
Exit ticket · 3 min
- Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
- 52 × 99 = ? → 5148Prompt: × 99 is × 100 then take away one lot.
- Use doubling and halving to work out 18 × 15. → 270Prompt: Halve 18 and double 15.
Watch out for
- Thinking multiplying always makes a number bigger.
- Dropping a zero in long multiplication when moving to the tens row.
Support and stretch
Support
- Review first: Multiply multiples of 10, 100 and 1000 mentally.
- Use concrete materials: counters for arrays.
- Give the first step of each question, or a partly worked example to finish.
- Pair with a confident partner for the guided practice.
Stretch
- Explain a common mistake in writing and how to fix it.
- Write a word problem that uses today's skill, then solve a partner's.
Homework and more practice
Free online practice with hints and printable worksheets for this skill: eurekami.com/math/grade-5.
Free lesson plan from eurekami.com/lesson-plan-builder