🎮 Complete the Proportion

📖 About this game

A game on solving proportions by cross multiplication, from the ratio and proportion chapter. The book text is its rule: a proportion is a statement in which at least two ratios or rates are equal, the cross products of any proportion are equal, and cross multiplication can also be used to find a missing value in a proportion, which is what solving a proportion means. Why three buttons rather than a keypad: a typed number is either right or wrong and tells you nothing, while each of the three shown numbers is a route through the mind, so picking one is a confession of the route the learner took. The two distractors are this lesson own mistakes and not random numbers: adding the difference instead of scaling by the ratio, which is the commonest beginner slip, and cross multiplying without the final division, which is the mistake of a learner who memorised the shape and missed the meaning. Half the rounds scale up and half scale down, because if the answer were always the largest number on screen the learner would stop calculating. The proof is hidden in the question and appears at the reveal, with the cross product itself framed in the table, because cross multiplication should be seen rather than told. Ten rounds. No sign-up.

🕹️ How to play

1. Read the table: two rows in two columns sharing one ratio.
2. Cross multiply, then divide by the number opposite the unknown.
3. Tap the number you reached.
4. Every proportion you get first try counts for you.