Cooking for more people? Times every amount by the same number. Fewer people? Divide them all.
Pancakes
👤 for 4 people
New batch
👤 for 16 people
The recipe is for 4 people. Make it for 16.
More people: times every amount by the same number.
Fewer people: divide every amount by the same number.
Stuck? Find the amount for 1 person first.
The amounts stay in proportion: the same recipe, just bigger or smaller.
A ratio compares amounts, like 2 eggs for every 1 cup of flour. Proportion means keeping that the same when you make more or less: for twice as many people you need twice the eggs and twice the flour.
Work out how many times bigger (or smaller) the new batch is, then multiply (or divide) every ingredient by that number. A recipe for 2 made for 6 is 3 times as big, so 2 eggs become 6 eggs.
Finding the amount for one first. If 3 people need 6 eggs, 1 person needs 6 ÷ 3 = 2, so 5 people need 2 × 5 = 10. It works even when the numbers don't scale neatly.
Children scale simple recipes and use 'for every' language at about 9 to 10, and learn ratio and proportion as a topic, including the unitary method, at about 10 to 11.