In this unit, students use their place value understanding and number sense to round numbers and to estimate sums and differences. Students will also use place value strategies, properties of operations, and the inverse relationship of addition and subtraction to find sums and differences within 1,000. Students will understand that perimeter of a polygon is the sum of the side lengths, and will find the perimeter given the side lengths. They will solve real world and mathematical problems involving perimeters of polygons. Students will use estimation to judge the reasonableness of answers. Students may struggle with the terms “rounding up” and “rounding down” without a visual model such as a number line or hundred chart.
Unitataglance
Key concept: Rounding is based on place value, and may be used to gauge the reasonableness of calculations or may be used in place of a specific calculation. 
Key concept: We can use place value understanding to add and subtract using a variety of strategies. 
Key concept: Perimeter is the sum of lengths of the sides of a polygon. 


Suggested pacing 
Days 16 
Days 712 
Days 1317 
Suggested class plan 



Additional unit information
Prior Knowledge Needed:
 Represent whole numbers on a number line diagram with equally spaced points and recognize the distance and proximity from other numbers; (Grade 2, Unit 3; 2.MD.B.6).
 Use place value understanding and properties of operations to add & subtract; (Grade 2, Unit 11; 2.NBT.B.6).
 Use concrete models and drawings to understand that it is sometimes necessary to compose and decompose numbers when adding and subtracting; (Grade 2, Unit 11; 2.NBT.B.7).
Units on the Horizon:
 Solving addition and subtraction problems involving measurements (Grade 3, Unit 5: 3.MD.A.1, 3.MD.A.2).
 Investigating patterns in number and operations (Grade 3, Unit 8: 3.NBT.A.1).
 Applying place value concepts in whole number addition and subtraction (Grade 4, Unit 1: 4.NBT.A.3).
Lessons, practice, & assessment