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Write common factors of 4 & 18
**

We find factors of 4 & 18 separately

So, Common factors of 4 & 18 are
**
1, 2
**

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Write common factors of 4 & 15
**

We find factors of 4 & 15 separately

So, Common factors of 4 & 15 are
**
1
**

Note:

If two numbers have common factor 1

Then, they areco-prime numbers

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