Challenge Level

*If you are a teacher, click here for a version of the problem suitable for classroom use, together with supporting materials. Otherwise, read on...*

If you had to work out $23 \times 21$ how would you do it?

What if you needed to work out $246 \times 34$?

Here are eight videos showing four different methods for working out the two multiplications. Can you make sense of them?

**Grid Multiplication**

$23 \times 21$

$246 \times 34$

**Column Multiplication**

$23 \times 21$

$246 \times 34$

**Multiplying with Lines**

$23 \times 21$

$246 \times 34$

**Gelosia Multiplication**

$23 \times 21$

$246 \times 34$

Once you have watched the videos, make up some multiplication calculations of your own and have a go at answering them using all four methods. Check that you get the same answer each time!

**Here are some questions to consider:**

Why does each method work?

What do the methods have in common?

What are the advantages and disadvantages to each method?

**Extension challenge**

Here is a video of another multiplication method, one where no writing down is needed along the way. Can you make sense of the video, and explain how this method works?