proportional

Everyday

1. In maths, two amounts are proportional if they grow or shrink together at the same rate, so that one is always the same number times the other. tree →
2. Proportional means having the right size or amount compared with something else, fair in size. tree →

In the lessons

In maths lessons, if 1 pencil costs 20p then 5 pencils cost 100p — cost is directly proportional to the number of pencils; the graph is a straight line through zero. Recipes and maps use proportion too. In ethics and law, a punishment should be proportional to the wrong done. In politics, «proportional representation» gives parties seats in proportion to their votes. Common phrases: «directly proportional», «inversely proportional», «proportional to», «proportional representation».

Examples

• The cost is proportional to the number of tickets you buy. tree →
• If you double the recipe, keep the ingredients proportional. tree →
• The time taken is inversely proportional to the speed. tree →
• Her drawing of the face was nicely proportional. tree →
• The punishment should be proportional to what he did wrong. tree →
• On a graph, proportional amounts make a straight line through zero. tree →
• New Zealand uses a kind of proportional representation in elections. tree →

Note

Use «proportional to». In maths: «directly proportional» — when one doubles, the other doubles; «inversely proportional» — when one doubles, the other halves (more workers, fewer days). Trap: amounts that both increase are not always proportional — the ratio must stay the same (for example, a taxi with a starting fee is not proportional).