Chapter 1 - Whole Numbers - 1.2 Adding Whole Numbers - 1.2 Exercises - Page 18: 7

$318+151+420=889$

First, add the digits in the ones column (each number's ones place) to determine the digit in the ones place of the sum: $8+1+0=9$ Next, add the digits in the tens column (each number's tens place) to determine the digit in the tens place of the sum: $1+5+2=8$ Then add the digits in the hundreds column (each number's hundreds place) to determine the digit in the hundreds place of the sum: $3+1+4=8$ If the sum has $8$ in the hundreds place, $8$ in the tens place and $9$ in the ones place, it must be $889$.