Lesson 4: Round Whole Numbers

Property

To round a number, first find the two benchmark numbers (e.g., the two thousands) it is between. Then, find the midpoint.
If the number is greater than or equal to the midpoint, round up to the next benchmark.
If the number is less than the midpoint, round down to the lower benchmark.

Examples

• To round $36,812$ to the nearest thousand: The number is between $36,000$ and $37,000$. The midpoint is $36,500$. Since $36,812 \geq 36,500$, we round up to $37,000$.
• To round $124,500$ to the nearest ten thousand: The number is between $120,000$ and $130,000$. The midpoint is $125,000$. Since $124,500 < 125,000$, we round down to $120,000$.
• To round $750,000$ to the nearest hundred thousand: The number is between $700,000$ and $800,000$. The midpoint is $750,000$. Since $750,000 \geq 750,000$, we round up to $800,000$.

Explanation

This skill involves rounding larger numbers to a specific place value like the thousands, ten thousands, or hundred thousands. First, you identify the two multiples of that place value that your number falls between. Then, you determine the halfway point, or midpoint, between them. If your number is at or above the midpoint, you round up; otherwise, you round down.

Property

How to round a whole number to a specific place value:

1. Locate the given place value.
2. Underline the digit to the right of the given place value.
3. Determine if this digit is greater than or equal to 5.
   • Yes: add 1 to the digit in the given place value. Handle any regrouping (like 9 becoming 10).
   • No: do not change the digit in the given place value.
4. Replace all digits to the right of the given place value with zeros.

Examples

• To round $4,862$ to the nearest hundred, look at the tens digit (6). Since $6 \ge 5$, round up the hundreds digit. The result is $4,900$.
• Rounding $12,345$ to the nearest thousand means looking at the hundreds digit (3). Since $3 < 5$, the thousands digit stays the same. The result is $12,000$.
• Rounding $49,850$ to the nearest thousand involves looking at the hundreds digit (8). Since $8 \ge 5$, we add 1 to the 9, which requires regrouping. The result is $50,000$.

Explanation

Rounding simplifies a number. Look at the digit just to the right of the place you're rounding to. If that digit is 5 or more, you round up. If it's 4 or less, you keep the digit the same.