Divisibility rules: 2, 3, 4, 5, 9, 10

A short test on the digits tells you whether a number divides evenly, without doing the division. A number is divisible by 3 when its digits add to a multiple of 3, by 4 when its last two digits are, by 5 when it ends in 0 or 5, and by 9 when its digit sum is.

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LearnWhat it is, how to spot it, a worked example, and where it goes wrong.
Practice — 3-point ladderNo problems written at this tier yet.Nothing written at this tier yet
Practice — 4-point ladder3 problems. Three in a row finishes it.0/3 in a row · 0/3 solved
Practice — 5-point ladderNo problems written at this tier yet.Nothing written at this tier yet
Skill quizFinish every ladder that has problems first.Finish the ladders above first

Before and after

Needs first

NUM-01Place value and digit positions

Opens up

NUM-05Factors, multiples, LCM and GCD by listing NUM-06Remainders and modular cycles

In official papers

No indexed official paper question has been tagged with NUM-04 yet. The index grows one paper at a time, and it records only question numbers, point values and our own skill tags — never the problems themselves.

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