We had a few solutions come in which showed how Catrina could work out how many football cards she has.

Joshua from Haslingfield Primary School wrote saying:

I used olive stones in five groups of four and counted them.

Georgia from Woodlea Junior School said:

I think the best idea of how to do this would be in your head because it's just 5 x 4.

Shree from The International School Frankfurt in Germany sent in this:-


 

Thank you for these ways of calculating, maybe you can see other ways.