som, verschil, product en quotiënt https://www.youtube.com/watch?v=XKvW6lxmO4I
Rekenvolgorde https://www.youtube.com/watch?v=x9YLphimBn0
Afronden https://www.youtube.com/watch?v=suJ-C8Sv3tU
Handige maten https://www.youtube.com/watch?v=hrg6fKe-G10