Children learn the dynamics of addition and subtraction through visual aid. These double-value flash cards in vertical format consist of 81 cards printed two sides, one side printed with an addition problem and the other side with a directly related subtraction problem (e.g. 3+1=4 on one side, 4-1=3 on the reverse). For every addition fact, there are three other facts that belong to the same family. Suggested activities included.