Which is greater. 8.72 or 8.720

Actually neither is greater.

these two numbers are equal to each other.

All because 8.720 has an extra number doesn't mean its greater. Because the number place is 0 is gives no significant value and is therefore the same as 8.72.

The bottom line is ...

8.72 = 8.720

Both answers are equal. There is no difference to both of them.