Three-Digit Addition

Three-Digit Addition

The strategy for adding three-digit numbers is the same as for adding two-digit numbers: you add from left to right. After each step, you arrive at a new (and simpler) addition problem. Let’s try the following:

                                                473

                        +326(300+20+6)

Starting with 473, we add 300, then add 20, then add 6. After adding 300 (473 +300=773), the problem becomes 773+26. After adding 20 (773+20=793), the problem simplifies to 793+6=799. This thought process can be diagrammed as follows:

473  +  326  =  773  +  26   =  793  +  6  =  799

                      +300                        +20                   +6

Let’s try another one for practice:

                                                   568

                         +496(400+40+6)

Then,

568  +  496  =  968  +  96   =  1058  +  6  =  1064

                        +400                      +90                   +6

This addition problem is a little more difficult than the last one since it requires you to carry numbers in all three steps. However, with this particular problem you have the option of using an alternative method. I am sure you will agree that it is a lot easier to add 500 to 759 than it is to add 496, so try adding 500 and then subtracting the difference:

                                                  568

                        +496(500-6)

Then

568  +  496  =  1068  -  4  =  1064

                       ( First add  +500)          ( then subtract  -6  )                               

Practice the following three-digit addition exercises,

1.      345 + 451  =

       2.   673 + 496 =

.      3.   786 + 429 =

    4.    369 + 345 =

    5.    281 + 496 =