Example 1: find 4673 – 2198.

Method:

(a) Write down what you need to make each digit in the second number up to 9: i.e. 7801.

(b) Add this to the first number:

4673

+

__7801__

12474

(c) Delete the 1 at the front of this and add it to the final digit: 2475.

That's the answer!

Make sure the two numbers have the same number of digits, by putting in leading zeros if necessary:

Example 2: find 5018 – 846.

Rewrite this as 5018 – 0846. Then using the method above ...

5018 – 0846

+

__9153__

14171 giving the answer 4172 (by deleting the 1 at the front of 14171 and adding it to the final digit.)

It works with decimals as well!

Example 3: find 6.254 – 0.98.

Rewrite this as 6.254 – 0.980

6.254 – 0.980

+

__9.019__

15.273 giving the answer 5.274 (by deleting the 1 at the front of 15.273 and adding it to the final digit.)

Try it! It really works.

But can you explain why??

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