These flashcards are designed to be able to print as double sided cards, with one addition fact on the front and the related subtraction fact on the back. In this way, students can learn about the three numbers within the fact family. Middle number questions are based on knowing the doubles facts - when the two numbers in the question are just two apart when counting (ex. 4+6 counts 4,5,6), take the middle number and double it (ex. 4+6 = 5+5) to find the answer. This can also be explained by taking one away from the larger number and adding it to the smaller number. Facts go from 1+3 / 4-1 to 7+9 / 16-9.