Reading a pictograph

A pictograph shows data with pictures. Each row is one category, and a small symbol is drawn again and again. Every pictograph has a key (or scale) that tells what one symbol stands for. Sometimes one symbol is 1 student; often it is many. If one smiley face stands for 10 children, a class of 50 needs only 5 faces, not 50.

Nand Kishor asks the children of his middle school in Berasia how often they sleep at least 9 hours at night. His key: 1 symbol = 10 children.

• 'Always' has 5 symbols: 5 × 10 = 50 children.
• 'Sometimes' has 2 whole symbols and a half: 2 × 10 = 20, and half a symbol is half of 10 = 5, so 20 + 5 = 25 children.
• 'Never' has 4 symbols: 4 × 10 = 40 children.

To read a pictograph: count the symbols in a row, multiply by the key, and add half the key for a half symbol. Then compare rows: the row with the most symbols is largest, the one with the fewest is smallest. Add rows for totals; subtract them for differences.

The key matters! In the book's pictograph of girl students, 1 symbol = 4 girls. Class 7 has 3 symbols, so it has 3 × 4 = 12 girls, not 3.