lessonfieldWhat they’re learning
Your child is learning to calculate flexibly in their head and to estimate before or after calculating. Useful strategies include making tens or hundreds, breaking numbers apart, and rounding to friendly numbers.
Explain it to my child
Mental math is about making a problem friendlier. For 198 + 35, think 200 + 35 = 235, then take away 2 to get 233.
Try it together
Play “about how much?” with grocery prices or numbers you invent. Before calculating exactly, each person gives an estimate and explains the friendly numbers they used.
Practice
- Estimate 392 + 211 to the nearest hundred.
- Mentally solve 99 + 46.
- Mentally solve 250 - 98.
- Is 487 + 312 closer to 700, 800, or 900?
- Give a reasonable estimate for 604 - 287.
Check understanding
- Can your child explain a mental strategy rather than only give an answer?
- Can they tell whether an exact answer is reasonable using an estimate?
Parent answer guide
- About 600
400 + 200. - 145
Add 100 then subtract 1. - 152
Subtract 100 then add 2. - 800
487 + 312 is 799. - About 300
600 - 300 is a useful benchmark.
Ontario curriculum connection
Grade 3 · Mathematics
Number · Operations
Curriculum expectation: Specific expectation omitted because Lessonfield has not yet verified an expectation-level mapping for this guide.