Number (add/sub)
UK Primary (3-6)
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Use strategies to add/subtract across the 100
Lesson

Remember that you can use several strategies to add and subtract 2-digit numbers.  You can use those same strategies to add and subtract numbers in the hundreds as well.  Read each strategy and watch the example videos.  Then decide which one you like the best!

Bridge to 10 and 100

Do you remember how to use the strategy of bridge to ten?  You can also bridge to the next hundred to make adding easier.  Watch how in the video below.  How is bridging to 100 like bridging to 10?  How is it different?

compensation

Do you remember what the word compensate means?  Return to the lesson on compensation if you've forgotten how to use that strategy to add and subtract.  Then, watch the video below to see how you can apply it to $3$3-digit numbers.

number line

You can place any number on a number line, even numbers in the hundreds!  You may find this strategy helpful for adding and subtracting numbers in the hundreds.  

Watch the video below to see some examples how.  If you need help, you can always go back and read the first lesson on the number line strategy.

Tips for Success

When adding to a number, jump forward (to the right).

When subtracting from a number, jump backwards (to the left).

Worked Examples

question 1

We want to find $8+493$8+493.

  1. First, split up $8$8 so that we have a pair to $10$10.

    $493$493 $+$+ $8$8 $=$= ??
    $|$| $\frown$
    $493$493 $+$+ $\editable{}$ $+$+ $\editable{}$ $=$= ??
    $\smile$
    $500$500
  2. Use the bridge to ten above to find $493+8$493+8.

question 2

Use the number line to find the answer to $163-9$1639.

  1. First place the bigger of $163$163 and $9$9 on the number line.

    160161162163164165166167168169170
  2. Use the position of $163$163 to find the place of $163-9$1639 on the number line.

    150152154156158160162164166168170

question 3

If $180-13=167$18013=167, what is the answer to $182-13$18213?

 

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