43 rounded to the nearest ten is 40. In 43, 3 is in the ones place and 4 is in the tens place. We look to the digit in the ones place to determine if we round up or down. If the digit is less than 5, round down; if it is greater than 5, round up. In our case, 3 is less than 5, so we round down to 40, since 40 is the nearest ten.
