P5 learn about ‘digital roots’ (repeated digital sum) to work out whether a number is a multiple of a certain times table.
How do you know a number is a multiple of six?
Step 1 –
The digital root is 3, 6 or 9.
e.g. Is 366 a multiple of 6? 3 + 6 + 6 = 15
Step 2 –
Take that number 15.
1 + 5 = 6, so 366 is a multiple of six.
Likewise –
How do you know a number is a multiple of nine?
The digital root is 9, e.g. 369 = 3 + 6 + 9 = 18 1 + 8 = 9,
so 369 is a multiple of nine.
How do you know a number is a multiple of three?
The digital root is 3, 6 or 9. e.g 369 = 3 + 6 + 9 = 18 1 + 8 = 9, so 369 is a multiple of 3.)
