Step by step
The question
Question: is 1290 divisible by 2, 3, 4, 5, 6, 9 and 10?
Divisible means it goes in exactly, with nothing left over.
1 Look at the last digit
1290 is 129 tens and 0.
2, 5 and 10 all go into 10, so into every ten.
Only the last digit is left to check.
For 2: is it even: 0, 2, 4, 6 or 8?
The last digit is 0.
So yes.
For 5: is it 0 or 5?
The last digit is 0.
So yes.
For 10: is it 0?
The last digit is 0.
So yes.
2 Look at the last two digits
100 is 4 times 25.
So 4 goes into every hundred.
Only the last two digits are left: 90.
90 divided by 4 is 22, with 2 left over.
So no.
Careful!
Even is not enough for 4.
1290 is even, but 4 does not go into 90.
3 Add the digits
We add the digits: 1 + 2 + 9 + 0 is 12.
Why add the digits?
Each ten is 9 and 1 more.
Each hundred is 99 and 1 more.
3 and 9 go into the 9s and 99s.
What is left over is the sum of the digits.
For 3: 12 divided by 3 is 4, nothing left over.
So 3 goes into 1290.
For 9: 12 divided by 9 is 1, with 3 left over.
So 9 does not go into 1290.
4 Use 2 and 3
6 is 2 times 3.
So 6 goes in only when 2 and 3 both go in.
Both do.
So yes.
5 Write the answer
So 1290 is divisible by 2, 3, 5, 6 and 10.
Not by 4 or 9.
6 Check
Let's check by dividing.
1290 divided by 2 is 645, nothing left over.
Every yes divides exactly, and 4 leaves 2 over.
The tests were right!
Let's look back.
First: look at the last digit.
Then: look at the last two digits.
Then: add the digits.
Then: use 2 and 3.
Then: write the answer.
Last: check.