Then Mr Frog got a piece of paper with a 10, 15, 20 numerals and the same amount of boxes underneath. He had to find different ways to make the number (10,15,20) and write it down. Colorful buttons helped him to visualize the addition.
To challenge him a little bit more I gave him number 40 and he tried some multiplication as well. With colorful buttons it was a piece of cake ;)