Quiz Entry - updated: 2026.07.14
When should you reach for each addition/subtraction shortcut?
Match the trick to the numbers: near a round value → round-and-adjust; two close values → count up; anything → left-to-right.
| Situation | Best tool |
|---|---|
| A number just below/above a round one (398, 497) | Rounding-and-adjusting |
| Subtracting two close numbers | Counting-up |
| Subtrahend near a round number (− 1.95, − 398) | Balancing |
| General, want to answer in reading order | Left-to-right |
They all rest on the same three algebra facts: addition regroups freely, and adding a constant to both sides of a subtraction (or over/under-shooting and correcting) leaves the true value intact.