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In this activity, we will add or subtract 100, 10 or 1 to or from a number.
When we add or subtract 100, it is the hundreds digit that we change.
When we add or subtract 10, it is the tens digit that we change.
When we add or subtract 1, it is the ones digit that we change.
Remember that other digits may have to change too.
Example 1
What number is 100 less than 750?
Answer
Reduce 7 hundred by 1 hundred to get 6 hundred...
750 becomes 650
Example 2
What number is 10 more than 539?
Answer
Increase 3 tens by 1 ten to get 4 tens...
539 becomes 549
Example 3
What number is 1 less than 539?
Answer
Reduce 9 ones by 1 one to get 8 ones...
539 becomes 538
Example 4
What number is 10 less than 405?
Answer
Here we have to be careful, because we can't reduce the tens digit by 1.
So include the hundreds digit.
Think of it as reducing 40 tens by 1 ten to get 39 tens.
405 becomes 395
That was a hard one to finish with, so make sure you've understood it before attempting the questions.
You can look back at this introduction at any point by clicking on the red help button on the screen.
