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Factor Lines

Arrange the four number cards on the grid, according to the rules, to make a diagonal, vertical or horizontal line.


Can you find a relationship between the number of dots on the circle and the number of steps that will ensure that all points are hit?

Factor Trio

Which of the numbers shown is the product of exactly 3 distinct prime factors?

Strange Numbers

Age 11 to 14 Challenge Level:

We define "strange" numbers in the following way:

  • All strange numbers are prime.
  • Every single digit prime number is strange. 
  • A number with two or more digits is strange if, and only if, the two numbers obtained from it, by removing either its first or its last digit, are also strange.

Find all strange numbers.

This problem comes from the Hungarian magazine KoMaL. You can find many other challenging problems in English on the KoMaL website.