Answer: 670
To round 660 to the nearest 10, you look at the digit in the tens place, which is 6 in this case.
Since the digit in the ones place is 0-4, we round down. If it is 5 or more, we round up.
In this case, 6 is greater than 5, so we round up the tens place to the next higher number.
Therefore, rounding 660 to the nearest 10, we get: 660 -> 670
