MAFS.3.NBT.1.1: Use place value understanding to round whole numbers to the nearest 10 or 100.
MAFS.3.OA.4.8: Solve two-step word problems using
the four (addition or subtraction) operations. Represent these problems using equations with a letter (symbol) standing for the unknown quantity. Assess the reasonableness of answers using mental computation and estimation strategies including rounding.
In 3rd grade, students are introduced to the concept of rounding and explore rounding numbers to the nearer 10 and 100. This introduction focuses on strengthening our students’ understanding of the value of numbers and should be grounded in students’ understanding of place value, not memorization of a rule.
Students need to consider the value of the digit in the ones and tens places to determine how to round a number to the nearest ten and the value of the digits in the tens and hundreds places to round a number to the nearest hundred. Placing the number on a number line between the closest tens or the closest hundreds will help students to see whether the number is closest to the given ten or the next ten (or hundred). Using the midpoint as a benchmark on the number line will help students to determine the closer ten or hundred.
The instructional strategies in this unit address the rounding of numbers through place value experiences and a focus on number sense. Using number lines, or building numbers with base-ten blocks, allows the students to visualize the number and find a close, but friendlier, number. Posing problems in context promotes students’ understanding of when rounding numbers is appropriate.
GCG 1 – Learning Goal: As a mathematician,I will be able to use strategies to fluently multiply by 3 (Ongoing Fluency)
- Step 1: Connect doubles plus 1 more group (triples) to gain fluency with ×3 facts
- Step 2: Decide when to apply the Commutative property and use other known facts for efficiency (e.g., students already know 53, they wouldn’t need to use the doubles plus one strategy)
GCG 2 – Learning Goal: As a mathematician,I will be able to use place value to round numbers to the nearer ten
- Step 1: Use base ten blocks to model the concept of rounding and relate rounding to number lines
- Step 2: Identify the midpoint between two tens on a number line and use the midpoint to round 2-digit numbers to the nearest ten
- Step 3: Identify the midpoint between two tens on a number line and use the midpoint to round 3-digit numbers to the nearest ten
GCG 3 – Learning Goal: As a mathematician,I will be able to use place value to round numbers to the nearer hundred
- Step 1: Use a number line to identify benchmark hundred values and midpoints of a 3-digit number
- Step 2: Use the midpoint to determine which hundred a 3-digit number is closest to (i.e., round 3-digit numbers to the nearest hundred)
- Step 3: Round 3-digit numbers to the nearest ten and hundred (including when the digit to the left is also affected (e.g., round 199 to the nearest ten)
GCG 4 – Learning Goal: As a mathematician,I will be able to use rounding to estimate sums and differences
- Step 1: Identify important information and retell a problem using your own words
- Step 2: Identify which operation(s) and the steps it would take to solve a two-step problem
- Step 3: Use rounding to estimate a sum(s) or difference(s), including with two-step problems