Problem of the Day
One good problem, every morning.
A fresh problem unlocks each day. Log in to solve it, then see how everyone else approached it.
Problem of the Day
The Complement MethodMON 19 OCTMedium
The Complement Method Problem
How many ways are there of using diagonals to divide a regular -sided polygon into triangles such that at least one side of each triangle is a side of the original polygon and that each vertex of each triangle is a vertex of the original polygon?
Limi: Missed a day? Every past problem, with its full solution, waits in your archive once you log in.
How it works
Small habit, big difference.
01Try it firstA new problem unlocks every morning. Work on it yourself before you look at anything else.
02Compare approachesOnce you solve it, read the solution and see in the thread how other students broke it open.
03Keep the streakOne problem a day adds up. Your streak shows how many mornings in a row you showed up.
Why an account
Everything in one place.
- Today's problem, every morning
- Your answer checked the moment you submit
- The solution and discussion thread once you solve it
- Your current and longest streak
- An archive of past problems to practise on
Ready for today’s problem?
Create your account in about two minutes. No preparation needed.
Already have one? Log in