Transcript Nines and threes

Nines and threes
I am learning to decide if a number is divisible by nine or three.
Can the number be shared evenly between 9 or 3.
To work out whether a number is divisible by nine add the digits
together. If the number you make is on your nine times table then
your original number is divisible by nine.
e.g. 72
7 + 2 = 9, 9 is on my 9 times table so 72 is divisible by 9.
Let’s find out why this works.
72 is shown below.
If we remove 1 from all the groups of ten then they will all have 9.
9 can easily be shared between 9 (9 ÷ 9 = 1)
You can see from this
that 72 is divisible by 9.
Now there are 9 ones left. (9 ÷ 9 = 1)
72
10
9
10
9
10
9
10
9
10
9
10
9
10
9
7
+
2
=9
Can 119 be divided by 9?
119 is shown below.
If we remove 1 from the 100 we will have 99. This amount can be
evenly shared between 9 (99 ÷ 9 = 11)
If we remove 1 from the group of ten we will have 9 in the group.
This amount can be shared between 9 (9 ÷ 9 = 1) .
Now there are 11 ones left. 11 can’t be evenly shared among 9
groups so 119 is not divisible by 9.
119
1
100
99
10
9
+
1 +
9
= 11
So 119 is not divisible by 9
Use this strategy to work out whether the numbers below are
divisible by 9. The first one has been done for you.
1) 333
Yes, (3 + 3 + 3 = 9)
2) 252
Yes, (2 + 5 + 2 = 9)
3) 114
No, (1 + 1 + 4 = 6)
4) 432
Yes, (4 + 3 + 2 = 9)
Click again when you have worked out
all your answers.
5) 227
No, (2 + 2 + 7 = 11)
Need some more practise? Try Pg47 & 48 of Teacher Tools Multiplication
and Division Book Numeracy resources