Snoot and Fin use near doubles to help them add two similar numbers.
NARRATOR: Hello everyone.
What are you doing?
SNOOT: (ALIEN LANGUAGE)
NARRATOR: Playing with your stacking meebs, of course.
How many meebs in your stack, Snoot?
SNOOT: (ALIEN LANGUAGE)
NARRATOR: 18! Very impressive.
What about your stack Fin?
FIN: (ALIEN LANGUAGE)
NARRATOR: 20 meebs! Wow!
That’s even more than Snoot.
I’ve got an idea.
Why not stack all your meebs together to make one super stack?
BOTH: Aha!
NARRATOR: If you add 20 to 18, how many meebs will you have altogether?
SNOOT: Er… Uh…
NARRATOR: Don’t worry Snoot.
You’ve almost got the same number of meebs, so you can work it out by doubling your 18, and then adding 2, because Fin’s got 20, 2 more than you.
2 times 18 makes 36, add 2 equals 38 meebs all together.
FIN: (ALIEN LANGUAGE)
NARRATOR: Well, if you’ve got another way of doing it Fin, go ahead.
Ah, I see.
You prefer to double your 20 meebs first, and then take away 2, because Snoot’s 18 meebs is 2 less than your 20.
2 times 20 makes 40, take away 2 equals…
38 again.
SNOOT: (ALIEN LANGUAGE)
NARRATOR: I know Snoot, it’s exactly the same as what you had before.
2 times 20 take away 2 is the same as 2 times 18 add 2.
BOTH: Aha!
NARRATOR: Right then, time to take down your stacks and make one super stack.
PLIMBLE: Plimble!
NARRATOR: Now that really is a stack!
Yours is still very good…
Ah…
Are you good at doubling numbers? This can help you add numbers that are close to each other.
The trick is to double a number that you know and then add on or take away the difference.
If you know that 10 + 10 = 20 then this can help you work out 10 + 11.
10 + 11 is the same as 10 + 10 + 1 which makes 21.
Example
9 + 12 = ?
9 and 12 are both close to 10.
10 + 10 = 20
9 is 1 less than 10, so take this away.
20 – 1 = 19
That leaves the 12. It is 2 more than 10 so you need to add this on.
19 + 2 = 21
You’ve just worked out that 9 + 12 = 21.
Which way round should I add two numbers? video
Fin and Snoot add up some of their favourite snacks: space grubs and astro bugs.
How can reordering numbers into number bonds help me add them? video
Snoot and Fin rearrange numbers and make number bonds when adding moons.
Find more 1st Level resources from BBC Bitesize
First Level is a stage of Scotland’s Curriculum for Excellence.
More on Numbers and number processes
Find out more by working through a topic
- count11 of 25
- count12 of 25
- count13 of 25
- count14 of 25
