I am less than 25. My ones digit is twice my tens digit. My digits add up to an even number.
An odd version of tic tac toe
In how many different ways can you break up a stick of 7 interlocking cubes? Now try with a stick of 8 cubes and a stick of 6 cubes.
Pat has 17 sweets in her bag. Rebecca found the next solution by
taking groups of five sweets away at a time - number 12 doesn't
work. Why doesn't 12 work?
Alistair from Histon and Impington Infants School said:
We know that the number of sweets is odd, because she has one
left over when she counts in twos but 7 does. She could have 7
sweets or she could have 17 sweets, but she can't have 12 because
it is an even number. There are no other numbers under 20 that fit