The big picture
Eight ideas, one habit. Find the height before you multiply.
| Idea | Remember | Example |
|---|---|---|
| Counting squares | Part squares count as the part they hold | 8 whole + 4 part = 12 |
| A rectangle | Length × width, whole or not | 9 × 4.5 = 40.5 |
| Cut and slide | Base × height | 8 × 4 = 32 |
| Half a parallelogram | Half of base × height | ½ × 10 × 6 = 30 |
| The height | Square across, not the slant | 8 × 5 = 40, not 48 |
| A trapezium | Average the parallel sides × height | 9 × 4 = 36 |
| Awkward outlines | Split, then add or take away | 40 + 16 = 56 |
| Square units | Use the side change twice | 100 × 100 = 10,000 |
Part II, Chapter 7 is Area. Your book goes further, with areas of triangles and other four-sided shapes.