When counting elements of a set, we need to make sure we don't count some of them twice. In how many ways can Sekou avoid trouble?
5,791 people working on this
Doctor Brilliantstein wants her creation's feet to support as much weight as possible. How can she achieve her goal?
11,863 people working on this
To fill in a graph so that adjacent regions are different colors, we need at most 4 colors. Is this true for a graph that’s been partially filled in?
6,721 people working on this
This Calcdoku doesn’t have many clues, but that can make it easier to find a place to start. Which gives you more information — a sum or a product?
7,314 people working on this
A newscaster is interviewing four people who won the lottery. How much did an interviewee win, and which state are they from?
7,232 people working on this
In cities, we often care more about walking than absolute distances. What's the optimal place for Xavier's cafe?
8,338 people working on this
In this game, players move a token across a square grid. Do we know the winner before the game even starts?
11,217 people working on this