Day 1 challenge

Day 2 challenge

Isosceles Triangles Poster

Isosceles Triangles Poster - February 2005

American Billions Poster

Age 11 to 14 Challenge Level:

Why?

First try 258:

The remaining possibilities are 1472589630 and 7412589630, but neither of 1472589 and 7412589 are divisible by 7

Next try 654:

The remaining possibilities are 1836547290, 1896543270, 1896547230, 7896543210, 3816547290, 9816543270 and 9816547230

Out of 1836547, 1896543, 1896547, 7896543, 3816547, 9816543 and 9816547, only 3816547 is a multiple of 7.