Number Series
Eighteen sequences to complete. Exactly one possible rule each time.
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About this test
Completing a number sequence is the oldest exercise in reasoning tests, and it survives for a good reason: it needs no knowledge beyond the four operations, yet it demands that you form a hypothesis, test it against every term, and drop it when it fails.
Every sequence here admits exactly one defensible continuation. Ambiguous sequences — the ones you can justify three different ways — have been deliberately left out, because they stop measuring anything other than luck.
The method that cracks the large majority of cases, in this order: write the differences between neighbouring terms; if they say nothing, look at the ratios; then the differences of the differences; then check whether each term comes from the two before it; finally, look for two interleaved sequences, one on the even positions and one on the odd. It also helps enormously to know by heart the squares up to 15, the cubes up to 6, the primes below 50 and the first few factorials.
How it works
Eighteen sequences in rising order of difficulty, four options each, no timer. Your score is the percentage of correct answers, and the rule behind every sequence is explained at the end.
This test is provided for entertainment purposes only. It is not a diagnosis or professional advice.