Represent and solve problems involving addition and subtraction.
1.OA.1 Use strategies to add and subtract within 20 to solve word problems involving situations of adding to, taking from, putting together, taking apart, and comparing, with unknowns in all positions.
1.NBT.6.i Use concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction to subtract multiples of 10 in the range of 10-90 from multiples of 10 in the same range resulting in a positive or zero difference.
1.NBT.6.ii Use a written method to explain the strategy.
Written method: an informal recording of a process or observation and may include narrative writing, numbers and symbols, pictures, equations, etc.
1.MD Measurement and Data
Measure lengths indirectly and by iterating length units.