Students have difficulty mastering subtraction facts because they do not link
them to addition facts. Students may know that 6 + 7 = 13 but fail to realize
that this fact also tells them that 13 – 7 = 6.
Students can add 36 + 16 = 52 but cannot use addition to help estimate a
difference, such as 52 – 36, or check the difference once it has been computed.