Watch: Adding or subtracting 10
This video explains how you can work out a calculation by adding or subtracting to 10 first.
Snoot and Fin use bridging through ten to add and subtract shells at the beach.
NARRATOR: Hello Snoot, hello Fin.
What a great sand castle!
SNOOT: (ALIEN LANGUAGE)
NARRATOR: You're going to decorate it as well. What with?
SNOOT: (ALIEN LANGUAGE)
NARRATOR: Lesser spotted splarkle shells.
Very decorative.
How many shells do you have?
You've got 5 splarkle shells Snoot, and Fin, you've got 7.
How many shells is that altogether?
SNOOT: Er… Oh…
NARRATOR: Don't worry Snoot.
A handy way of working out 5 add 7 is to make 10 first.
Take your 5 shells Snoot, and add 5 from Fin's 7, which equals 10.
That leaves 2 shells left over.
So just add 2 to 10 and what do you get?
12 shells all together.
FIN: (ALIEN LANGUAGE)
NARRATOR: Oh right, Fin.
You only need 6 shells to decorate your sand castle.
That means you can take away 6 from 12 and just leave the rest.
How many does that leave?
FIN: (ALIEN LANGUAGE)
NARRATOR: OK Fin, you want to take away 6 from 12 by counting back through 10 as well.
12 minus 2 equals 10, so to get 10, just take 2 of the 6 shells away.
That leaves you with 4 shells to take away.
And what's 10 take away 4?
That's right, 6!
BOTH: Aha!
NARRATOR: But how do you know which shells to use and which to leave?
(POP)
NARRATOR: Ah… Maybe you should just leave them all?
Bridging through 10
Adding by making 10 is also called bridging through 10.
Here's what to do:
Work out what you need to add to your first number to make ten.
Take this from your second number. What do you have left?
Add what is left to 10. That's your answer!
Example 1
Method 1
8 + 4 = ?
This can be solved by partitioning one of the numbers.
Here are two tens frames showing 8 orange counters.
Here are 4 yellow counters which are going to be added to the 8 orange counters.
There are 2 empty spaces on the left hand ten frame.
8 + 2 = 10
We have used 2 of the yellow counters to make 10.
There are 2 yellow counters left over that are added to the second ten frame.
10 + 2 = 12
This shows 8 + 4 = 12
Method 2
The same calculation can be solved using the part-whole model.
4 can be split into 2 and 2.
2 can be added to 8 to make 10.
8 + 2 = 10
Then the 10 can be added to the other 2 to make 12.
10 + 2 = 12
Which means 8 + 4 = 12
Example 2
7 + 4 = ?
Start by working out what you need to add to 7 to make 10.
7 + ? = 10
The answer is 3.
Take this answer away from the second number in the calculation.
4 - 3 = 1
Add this answer on to 10.
10 + 1 = 11
So:
7 + 4 = 11.
This can be shown as a part-whole model like this.
Activities
Quiz 1
Have a go at these quizzes to put what you've practised into action.
Quiz 2
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