Rule finder

How this works

Each item shows solved figures that share one hidden rule. The rule is plain arithmetic: adding, taking away, multiplying, halving, or adding up digits. Find a rule that fits every solved figure, then use it on the last one.

Test a rule on every solved figure before you answer. A rule that fits only the first figure is not the rule.

Level 1 shows three solved figures with numbers 1 to 9 and four answers to pick from. Level 2 shows two. Level 3 uses numbers up to 19. Level 4 adds figures with six numbers and harder rules, and you type the answer. Level 5 is a frame of twelve numbers around a square with one missing: either the middle number of every side is made from its two ends, or every number on the bottom row and in the right column is made from the number straight across the square from it.

Every item is checked before it is shown. No other rule we check fits all the solved figures, and the check includes about fifty common rules this practice never asks for, such as adding all but the largest number. The answer is never a number already on the screen. The four answers are evenly spaced numbers that the same rule gives to other figures, so their order and spacing do not point to the right one.

Your score is how many of the six you answered correctly. It is practice at finding rules, not a measure of ability. Finish the round to save it in this browser. Ending a round early saves nothing.

Press 1 to 4 or A to D to pick an answer. Type an answer and press Enter to check it. Enter then moves to the next item. Escape ends the round. End ends it too, except while the caret is in the answer box.