IN YOUR MATHS LESSON
Why not check your sums by this fascinating method using digit sums.
- Suppose you want to check that the simple
addition sum below is correct.
3 2 +
We find the digit sums of 43, 32 and 75 and check
that the first two digit sums add up to the third digit sum.
4 3 7
3 2 + 5 +
7 5 3
The digit sums are shown on the right and
7 + 5 = 3 is correct in digit sums because
7 + 5 = 12 = 3 (1 + 2 = 3)
This indicates that the answer is correct.
All sums, even the most complex, can be checked in this way.
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In Your Maths Lesson
It is worth noting (in case you want to check
subtraction sums using the nine-point circle) that in
digit sums 7-5=2, 6-6=0 and so on, but 3-4=8.
You can see this on the circle by starting at 3 and
going 4 jumps backwards round the circle.
Or, alternatively you can add 9 to the 3 so that 3-4
becomes 12-4, which is 8.
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