WA.2.2. Core Content: Addition and subtraction (Operations, Geometry/Measurement, Algebra) Students focus on what it means to add and subtract as they become fluent with single-digit addition and subtraction facts and develop addition and subtraction procedures for two-digit numbers. Students make sense of these procedures by building on what they know about place value and number relationships and by putting together or taking apart sets of objects. This is students' first time to deal formally with step-by-step procedures (algorithms) - an important component of mathematics where a generalizable technique can be used in many similar situations. Students begin to use estimation to determine if their answers are reasonable.
2.2.A. Quickly recall basic addition facts and related subtraction facts for sums through 20.