Rounding a number to the nearest hundred can be determined by the digit in the tenths place. If the digit in the tenths place is between 0 and 4, the number should be rounded down. If the digit in the tenths place is between 5 and 9, the number should be rounded up. In this case, the number has a digit in the tenths place that is between 5 and 9. Therefore, 684 should be rounded up to 700.
