Summary
Fixit with Karen!
Understanding what happens when we multiply by 10 or 100, means that we can apply this to our times tables facts to work out many other calculations mentally. It is especially important to work on understanding multiplying using place value for learners with dyscalculia as they need these links to be explicitly taught.
You can see how we teach multiplying by 10 in one of our previous videos here – https://www.youtube.com/watch?v=ut-hv9xNtmI. and blog here – https://dyscalculianetwork.com/multiply-by-10-for-learners-with-dyscalculia/
Make sure the learner has a secure understanding of both multiplying by 10 and with the relevant times tables facts before beginning work on this next step; as always making sure we build a firm foundation of pre-skills is essential.
When first presented with a calculation such as 6 x 20, children can tend to count in 20s six times. To introduce an alternative strategy, manipulatives can be used on a place value grid to show 6 x 2 = 12 as 6 groups of 2 ones in the ones place on the grid. Then 6 x 20 can be shown as 6 groups of 2 tens in the tens place. The two calculations can be compared, discussing what is different and what is the same. When multiplying by 20, we can see that this takes place in the tens place, rather than the ones – the 2 has been made 10 times larger, so the answer will be 10 times larger.
6 x 2 = 12, so 6 x 20 = 120
We can see that the digits in the answer have moved one place to the left and we need a place holder in the ones place. This is because 6 x 20 is the same as 6 x 2 x 10.
This understanding can then be applied to calculations such as 6 x 200. We can still see 6 x 2, but this time the 2 has been made 100 times larger, so the answer is also 100 times larger. This means that the digits have moved 2 places to the left and we need two place holders.
6 x 2 = 12, so 6 x 200 = 1200 because this is the same as 6 x 2 x 100
It is important to establish this understanding so that children with dyscalculia are fluent in applying place value to their times table facts before the written methods for multiplication are introduced.
