Stage 4 of 20
Adding Near Tens
Turn awkward addends like 9, 8, or 11 into friendly tens, then adjust. Compensation is a classic mental math shortcut.
Round, add, then compensate
To add 9, add 10 and subtract 1. To add 8, add 10 and subtract 2. To add 11, add 10 and add 1 more. Always finish with the adjustment.
Why this mental math skill matters
Compensation turns awkward addends like 9 or 8 into friendly tens. Kids gain a portable “trick” that is really a transparent strategy.
Worked examples
Study each example slowly. Say the steps aloud — verbal rehearsal strengthens mental arithmetic memory.
46 + 9
- 46 + 10 = 56.
- You added 1 too many.
- 56 − 1 = 55.
Answer: 55
37 + 8
- 37 + 10 = 47.
- Compensate by −2.
- 45.
Answer: 45
54 + 11
- 54 + 10 = 64.
- Add the extra 1.
- 65.
Answer: 65
Tips for success
- Add 10, then subtract the extra 1 or 2.
- For +11, add 10 then add 1 more.
- Check with a rough estimate before confirming.
Common mistakes to avoid
- Forgetting the final adjust step after rounding.
- Rounding the wrong direction when tired.
How to practice this stage
Practice +9 and +8 on random two-digit starts. Always finish with the compensation step so the habit sticks.
Interactive practice
Stage 4 Drill
Round to a ten, then adjust by 1 or 2.
Solve
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FAQ: Adding Near Tens
How do you add 9 mentally?
Add 10, then subtract 1. Example: 46 + 9 → 46 + 10 − 1 = 55.
Does compensation work for subtraction too?
Yes — Stage 10 revisits rounding and adjusting for two-digit subtraction.