Mental multiplication and division (age 9+)
Multiply and divide numbers mentally drawing upon known facts, including related facts and place-value adjustments
What a learner can do afterwards
- Calculate 40 × 60 mentally by using 4 × 6 = 24 then appending zeros
- Derive 7 × 15 by calculating 7 × 10 + 7 × 5
- Calculate 360 ÷ 9 mentally using 36 ÷ 9 = 4
1 · Read
You already know your times tables and division facts. You can use those same facts to solve much bigger problems in your head, just by paying attention to place value.
To work out 7 × 15, split 15 into 10 and 5. Then 7 × 10 = 70 and 7 × 5 = 35. Add them: 70 + 35 = 105.
To work out 360 ÷ 9, drop the zero and find 36 ÷ 9 = 4 first. Then put the zero back on your answer: 40.
Two tricks to remember: split a number into tens and ones and add the results, or drop a zero, use the smaller fact, then put the zero back on.
Break a big problem into a fact you already know, then adjust for the extra zero or the extra pieces.
2 · Watch
Take it off screen
Where it sits
Learn first
This opens up
17 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.