Test the assumption first. Then let the reasoning earn the answer.

Reasoning help

When the reasoning needs another step

These are the questions readers ask most. Each answer names the tempting assumption, then adds the missing step.

Patterns and proof

If a pattern works for the first five cases, isn't it proven?

No. Chords between points on a circle give 1, 2, 4, 8, 16 regions and then 31, not 32. A pattern becomes a rule only when you can explain why it must continue. See the full argument.

Why does the centre of a 3×3 magic square have to be 5?

Each line sums to 15. The four lines through the centre total 60 and cover all nine cells, with the centre counted four times. So 45 + 3c = 60 and c = 5. Worked example.

Strategy

What is backward induction?

Reasoning from the end of a game toward the start. You label each position as winning or losing for the player about to move, then pick moves that hand your opponent losing positions. Try the 21-stone game.

Is capturing the goal in Go?

Not directly. Score depends on territory (and, in area scoring, stones on the board). Captures matter when they change territory or the safety of groups.

Chance

After several heads in a row, is tails more likely?

For a fair coin, no. Each toss is independent, so the chance stays 1/2. Expecting otherwise is the gambler's fallacy.

Does this site give betting or gambling advice?

No. Probability content is educational. No strategy changes the built-in house advantage of commercial games of chance.

History

Was sudoku invented in Japan?

The format first appeared as "Number Place" in Dell magazines in the United States from 1979, credited to Howard Garns. The Japanese publisher Nikoli popularised it and named it Sudoku in 1984.

Is the tangram an ancient puzzle?

Its documented history begins with Chinese publications in the early nineteenth century. Claims of thousands of years of history are not supported by sources.

What are sangaku?

Wooden tablets of geometry problems hung in Japanese shrines and temples during the Edo period, often offered by amateurs. Read more.

Do I need advanced mathematics to use this site?

No. Most worked examples need arithmetic and careful counting. Writing every step down matters more than prior knowledge.

Still stuck? Ask a question and include what you tried — it helps us find the exact step that needs explaining.