Near-doubles: Sums such as 6 + 7 = 13 can be quickly derived from the doubles fact 6 + 6 = 12 by adding one more, or from 7 + 7 = 14 but subtracting one [REF].
Five and ten: Sums of the form 5 + and 10 + are usually memorized early and can be used for deriving other facts.