Answer key: Adding and Subtracting American Lengths
Companion answer key for the printable worksheet "Adding and Subtracting American Lengths" — Common Core CCSS.MATH.3.MD.A.1, Easy difficulty. Use it to spot-check during the lesson or grade afterward.
Sample answers
| # | Question type | Sample answer |
|---|---|---|
| 1 | 45 + 12 | 57 |
| 2 | 25 + 17 | 42 |
| 3 | 49 + 37 | 86 |
| 4 | 21 + 39 | 60 |
| 5 | 24 + 18 | 42 |
| 6 | 14 + 25 | 39 |
| 7 | 6 + 29 | 35 |
| 8 | 13 + 8 | 21 |
How to grade this worksheet
This answer key is intentionally short — eight items or fewer — so you can spot-check during the lesson rather than waiting until the end. For Math worksheets at the easy level, we recommend the following grading flow.
- Pencil-only spot check. Walk by every five minutes and circle (lightly) any item that looks off. Do not announce the score.
- Self-grade. When the student finishes, hand them this answer key and let them grade their own work in pen. Self-grading produces about 30% better retention than parent-grading at this age.
- Two-question debrief. Pick the two items they missed and ask: "Walk me through what you tried." Their explanation usually reveals whether it was a careless error or a genuine concept gap.
- Log the score. Note the score, the date, and the standard code (
CCSS.MATH.3.MD.A.1) in your portfolio. Three data points across a month is enough to know if the standard is mastered.
If the student misses more than half of the items, do not reteach the same way. Switch modalities — manipulatives, a drawn diagram, a verbal walk-through — and revisit a fresh worksheet on the same standard the next morning.