Number - Rounding to the nearest 10 or 100

Grade 3IGCSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

•

Understanding place value: identifying the ones, tens, and hundreds columns.

•

The 'Rounding Rule': If the digit to the right is 5 or more (5, 6, 7, 8, 9), round up. If it is less than 5 (0, 1, 2, 3, 4), round down.

•

Rounding to the nearest 10: Look at the digit in the ones place.

•

Rounding to the nearest 100: Look at the digit in the tens place.

•

Number line visualization: Identifying which multiple of 10 or 100 a number is closest to.

📐Formulae

\text{If digit} \ge 5 \rightarrow \text{Round UP}

\text{If digit} < 5 \rightarrow \text{Round DOWN (Keep the target digit the same)}

💡Examples

Problem 1:

Round 67 to the nearest 10.

Solution:

70

Explanation:

To round to the nearest 10, we look at the ones digit. The ones digit is 7. Since 7 is greater than or equal to 5, we round the tens digit up from 6 to 7 and change the ones digit to 0.

Problem 2:

Round 342 to the nearest 100.

Solution:

300

Explanation:

To round to the nearest 100, we look at the tens digit. The tens digit is 4. Since 4 is less than 5, we round down. This means the hundreds digit stays as 3, and the tens and ones digits become 0.

Problem 3:

Round 850 to the nearest 100.

Solution:

900

Explanation:

When rounding to the nearest 100, we check the tens digit. The tens digit is 5. According to the rule '5 or more, round up', we increase the hundreds digit from 8 to 9 and set the following digits to 0.

Problem 4:

Round 124 to the nearest 10.

Solution:

120

Explanation:

To round to the nearest 10, we look at the ones digit, which is 4. Since 4 is less than 5, we round down. The tens digit stays at 2 and the ones digit becomes 0.