Sixteen problems that all take away 5, from 5 − 5 all the way up to 20 − 5, with a number line from 0 to 20 along the bottom for counting back.
Working on one number at a time lets a child spot the pattern. Once they notice that 15 − 5 is 10 and 17 − 5 is 12, they stop counting and start knowing, which is the point.
The problems are mixed rather than in order, so the pattern has to be found rather than read off the page. Bright colored tiles keep it cheerful.