Stage 3 of 20
Left-to-Right Addition
Add from the highest place value first. Starting with tens (then ones) matches how we speak numbers and keeps working memory light.
Add tens, then ones
For 34 + 25, think “30 + 20 = 50” then “4 + 5 = 9,” then combine. Left-to-right addition reduces carry-over stress and builds place-value fluency.
Why this mental math skill matters
Left-to-right addition matches how we say numbers (“forty-two plus thirty-one”). Starting with tens keeps the magnitude clear and often feels easier than ones-first carrying for mental work.
Worked examples
Study each example slowly. Say the steps aloud — verbal rehearsal strengthens mental arithmetic memory.
42 + 31
- Tens: 40 + 30 = 70.
- Ones: 2 + 1 = 3.
- Combine: 73.
Answer: 73
56 + 23
- 50 + 20 = 70.
- 6 + 3 = 9.
- 70 + 9 = 79.
Answer: 79
18 + 41
- 10 + 40 = 50.
- 8 + 1 = 9.
- 59.
Answer: 59
Tips for success
- Say the tens sum before touching the ones.
- Keep a “running total” whispered after each part.
- If ones make more than 9, add that extra ten to your tens total.
Common mistakes to avoid
- Switching mid-problem to a different half-finished method.
- Adding ones first mentally and losing track of the tens.
How to practice this stage
Solve five two-digit sums by saying tens first, then ones. Use the drill to check accuracy, then try explaining one problem to a parent or sibling.
Interactive practice
Stage 3 Drill
Add the tens first, then the ones.
Solve
—
FAQ: Left-to-Right Addition
What is left-to-right addition?
It means adding the highest place value first (tens), then the ones, then combining — a core mental math addition strategy.
Is left-to-right better than the written algorithm?
Both are useful. Left-to-right is often clearer for mental calculation; written algorithms remain valuable on paper.