This includes 10 worksheets involving addition and subtraction. After the students solve the addition/subtraction problems, they are to write the corresponding letter to answer a riddle. There are 3 different types of worksheets: Addition/Subtraction, Adding Ten More, and Doubles Facts. In each of these categories there are worksheets for students working at different levels. There are 3 worksheets of single-digit addition/subtraction, there are 3 worksheets of adding ten more, and there are 2 worksheets of doubles facts.