Primes

About Primes

Two bowls sit at the bottom of the screen, one for prime numbers and one for non-prime numbers. Balls with numbers printed on them fall from the top, each headed toward one of the two bowls. You can swap the positions of the bowls by clicking and holding on one bowl, then releasing on the other. The goal is to route every falling ball into the correct bowl: prime balls into the prime bowl, non-prime balls into the non-prime bowl.

The challenge comes from speed and the constant need to reassess. The bowls swap only when you tell them to, so you must track which bowl is where and anticipate which ball type is falling where. As the game progresses, balls fall faster, forcing quicker decisions. A single wrong sort—a prime ball into the non-prime bowl or vice versa—ends the run. The mix of numbers may expand beyond 7 and 9, testing your ability to recognise primes under pressure.

Tips to win

• Watch the next ball early: identify its number and which bowl it's heading for, then decide if a swap is needed.
• Keep the bowls in their default positions when no ball is imminent to reduce confusion.
• For numbers other than 7 and 9, quickly test divisibility: even numbers (except 2) and multiples of 3 are not prime.