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D.2 Rounding: word problems

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What is rounding?

Rounding means changing a number to a nearby number that is easier to work with or understand. We usually round to the nearest ten, hundred, or thousand.

Examples:
  • 47 rounded to the nearest ten is 50
  • 132 rounded to the nearest hundred is 100
  • 2,789 rounded to the nearest thousand is 3,000
Note

Think of rounding like finding the closest landmark. If you're between two houses, you go to the one that's closer.

Rounding to the nearest ten

To round a number, look at the digit to the right of the place you're rounding to. If it's 5 or more, round up. If it's 4 or less, round down.

Steps for Rounding to the Nearest Ten:
  • Look at the number in the ones place
  • If it's 5, 6, 7, 8, or 9 → round up
  • If it's 0, 1, 2, 3, or 4 → round down
  • Example: 36 → ones digit is 6 → round up → 40
Note

When rounding up, the digit in the place you're rounding to increases by 1, and all digits to the right become zeros.

Rounding to the nearest hundred

When rounding to the nearest hundred, look at the tens digit. If it's 5 or more, round up. If it's 4 or less, round down.

Examples:
  • 247 → tens digit is 4 → round down → 200
  • 685 → tens digit is 8 → round up → 700
  • 350 → tens digit is 5 → round up → 400
Note

Numbers ending in 50 always round up to the next hundred. For example, 350 rounds to 400, not 300.

Solving rounding puzzles

Sometimes you'll need to figure out what a number could be based on how it rounds. These are called rounding puzzles.

Example Puzzle:
  • A number uses the digits 6, 5, and 2
  • To the nearest hundred, it rounds to 600
  • What could the number be?
Note

When solving rounding puzzles, think about all the possible numbers you can make with the given digits that would round to the target number.

Solving the example puzzle

Let's solve the puzzle step by step using the digits 6, 5, and 2.

Solution Steps:
  • We need a 3-digit number using 6, 5, and 2
  • It must round to 600 (nearest hundred)
  • For a number to round to 600, it must be between 550 and 649
  • Possible numbers: 562, 526, 625, 652
  • Check each: 562→600, 526→500, 625→600, 652→700
  • Correct answers: 562 and 625
Note

Some rounding puzzles have more than one correct answer. Always check all possibilities.