Today, in our live lesson, we will be subtracting two 2 digit numbers by counting back in 10s and 1s.
You will need a 100 square to help you with this. If you do not have one, why not have a go at making your own on a piece of paper.
Let's look at the number sentence 68 -27 =
Find the biggest number on the 100 square. Instead of doing ten little jumps back, remember you can do one big spider jump to the number above and that is 10 less. 27 has 2 tens so we will do 2 big spider jumps up to the numbers above to subtract the two tens in the number 27. We start on 68, the biggest number, and jump up to 58 to subtract one ten, then jump up to 48 to subtract two tens. See the picture below.
To subtract ones on the 100 square you do one more little jump back. There are 7 ones in 27, So we start at 48, where we landed after subtracting our tens, and do 7 little jumps back and we land on 41. Our answer is 68 - 27 = 41
Have a go at practising this with the chilli challenges below. If you complete them, you could make up some more of your own number sentences.
Abacus homework is now set for you - Toucan Team.
A paper copy of the homework is available to print below.