Two-Digit Addition Examples

Mental Math · Axiom Academy

EXAMPLE Adding 47 + 38 Left to Right Break both numbers into tens and ones, add the parts, and combine — using complements to bridge the ones quickly. Calculate 47 + 38 mentally using left-to-right addition — the same technique from the last lesson, now applied step by step. Well done — you've used left-to-right addition, just like the last lesson, to mentally add two two-digit numbers. Remember: Break both numbers by place value: add the tens together, then the ones together. Complements to 10 make the ones easy: bridge through the next ten instead of counting on one at a time. Combine the partial sums (tens-sum plus ones-sum) for the final answer. Regrouping doesn't change the total: you can add the parts of a sum in any order or grouping. You'll pick up even more mental-addition shortcuts — like compensation and other ways of breaking apart addends — in the lessons ahead.

This is the written version of the interactive lesson above. See the full Mental Math course.