Today we discussed easy ways to add or subtract numbers mentally (in our heads without pencil or paper or even a calculator). We discussed adding nine to numbers by adding ten then taking away one. Our challenge was to use a similar strategy to record other numbers that might be added or subtracted this way.
Lauren: To add 8 to any number you can add 10 then take away 2.
eg: 64 + 8 = 64 + 10 - 2 = 72
Jacob: To add 23 to any number you can add 20 and then add 3.
eg: 1 648 + 23 = 1 648 + 20 + 3 = 1 671
Tia: To add 13 to any number you can add 10 and then add 3.
eg: 674 + 13 = 674 + 10 + 3 = 687
Tessa: To take away 9 from any number you take away 10 and then add 1.
eg: 52 - 9 = 52 - 10 + 1 = 43
Tom: To take away 18 from any number you can take away 20 and then add 2.
eg: 147 - 18 = 147 - 20 + 2 = 129
Stephanie: To take 8 away from any number you can take away 10 and add 2.
eg: 63 - 8 = 63 - 10 + 2 = 55
Can you share any other numbers that might be added or subtracted in this way?
Our Term 3 Learning about Australian History
6 years ago
2 comments:
Hey Middles,
That's a fantastic skill to use when you are counting in your head. I like how you have all given clear examples. To take 3524 away from something round it up to 3550 by adding 26 thats a big example but I was just showing one. Hope you have a fun term! From Georgia M :)
Hi Middles,
Looks as though you are heading for Seniors fast! How about when you add 199 to something, add 200 and take off 1!
eg. 64 + 199 = 64 + 200 - 1 = 263!
Mrs Yore
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