Today in class, we are beginning to explore how to add and subtract 9, 10 and 11.
Remember, if you know how to add and subtract 10, then adding and subtracting 9 and 11 should be fairly simple!
Watch the video below to refresh your memory on adding and subtracting 10 (finding 10 more or less then any number)
Before you can add or subtract 9 or 11, you must practice adding and subtracting 10 and know how to do it really well!
Use our adding 9 strategy:
When you see +9, think 'add 10 and subtract 1'.
Use our subtracting 9 strategy:
When you see -9, think 'subtract 10 and add 1'.
Use our adding 11 strategy:
When you see +11, think 'add 10 and add 1 more'.
Use our subtracting 11 strategy:
When you see -11 think 'subtract 10 and subtract another 1'.
Now, have a go at at least 8 of these questions! The answers are attached too :)