Subitising is the ability to see a number of objects. We can subitise up to 5 or 6 items that are not in a known order but not usually much more than that. This skill is an important one as it is the beginning of building a sense of number. Lots of the aspects of subitising are foundations for our understanding of number and arithmetic. To begin with, let’s look at number bonds.
Most people would need to count this to tell how many dots there are. You can practise by subitising it in 2 parts. This would be one way:
It might be easier to detect the 3 and 4 there. If you know some addition facts, that would probably be enough to tell you the total.
You might find this easier though:
It’s the same 7 but it might be easier to see the 5 and the 2 (as the 5 is a recognisable shape).
Subitising can also help you enrich your experience of repeated addition, which is often used to introduce multiplication. You can take a larger number of objects such as pictured here:
This is well beyond the capacity of most of us to subitise but we can pick out smaller groups. Usually we’d group them in 2s, 3s or 4s. Let’s see it with 3s:
This way we can get to practise counting in 3s and work out how many objects there are.
Threes are usually possible to recognise because they form a 1 of two recognisable patterns nearly all the time. They can be a triangle or a straight line.
Playing Nim regularly is a really good way to start learning to subitise. In Nim, you lay out a number of objects and take turns to remove up to a particular number. To win you would have to start to recognise what one of our explorers called “danger numbers”. To do that you need as convenient a way as possible of telling how many objects there are.
Try exploring subitising by making cards that have ordered and unordered dots on them. Try this with numbers 7, 8 and 9 with a few other numbers thrown in for good measure. See if there are some that are easier to recognise than others. We’ve started the pack off for you (download it here) with a few random and a few recognisable sets of numbers. See how quickly you can recognise them. Can you find the cards which are exactly the same?