Left-to-Right Addition Method

Mental Math · Axiom Academy

Add the biggest place first and carry one running total in your head — a number you can say out loud as it grows. 1. One Running Total, Biggest Place First Take 34 + 33 . Add the tens first: 30 + 30 is 60. That 60 is your running total . Now slide right to the ones : 4 + 3 is 7, so the total climbs to 67. You never juggle two separate answers — you hold one number and let it grow. One total, updated left to right The only twist is a carry . Take 47 + 38 . Tens first: 40 + 30 is 70 — running total 70. Now the ones: 7 + 8 is 15 . That is a whole ten plus 5, so the ten rolls up into the total (70 becomes 80) and the 5 lands last: 85 . When a place spills past ten, you nudge the total up and keep moving. For 68 + 57 , the tens alone already pass one hundred: 60 + 50 is 110. Then 8 + 7 is 15, and 110 + 15 is 125 — the very same move, one place higher. 3. It Scales — The Leading Digit Lands First Big numbers work exactly the same way, and left-to-right shines here. Take 346 + 287 . Hundreds first: 300 + 200 is 500 — so you already know the answer is in the five-to-six hundreds . Tens: 40 + 80 is 120, nudging the total to 620 . Ones: 6 + 7 is 13, settling on 633 . The biggest digit lands first; the smaller places only sharpen it. You can now add from the left, holding one running total you can say out loud — often before you would have finished carrying on paper. Scroll up to revisit any step.

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