Missing addends, sums under 20 worksheets K5 Learning Missing addends, sums under 20 Single digit addition Single digit addition worksheets with missing addends. Good practice for students who are progressing well with their addition facts. 18 questions Worksheet #1 Worksheet #2 36 questions Worksheet #3 Worksheet #4 3 More 56 questions Worksheet #5 Worksheet #6 Similar: Complements of 9 Making 10