Rounding to the Nearest Ten
Rounding to the nearest ten means replacing a number with the closest multiple of ten — if a number is halfway between two tens, the rule is to round up. In 4th grade math with Saxon Math Intermediate 4, Chapter 2, students learn to look at the ones digit: if it is 0-4 they round down, and if it is 5-9 they round up. For example, 82 rounds to 80 (ones digit 2, round down) and 75 rounds to 80 (ones digit 5, round up). Rounding is the foundation of estimation, mental math, and checking reasonableness of answers.
Key Concepts
Property To round a number to the nearest ten, we choose the closest number that ends in zero.
Examples For example, $82$ is closer to $80$ than $90$, so it rounds to $80$. The number $47$ is closer to $50$. A number like $75$ is exactly halfway, so it rounds up to $80$.
Explanation Think of it like jumping to the nearest safety platform on a number line, where platforms are numbers like $10, 20, 30$. If you're exactly halfway between two, the rule is to always jump up!
Common Questions
How do you round a number to the nearest ten?
Look at the ones digit. If it is 4 or less, keep the tens digit the same and replace the ones digit with zero (round down). If it is 5 or more, increase the tens digit by 1 and replace ones with zero (round up).
What does 47 round to?
47 rounds to 50. The ones digit is 7, which is 5 or more, so you round up: 40 becomes 50.
What does 82 round to?
82 rounds to 80. The ones digit is 2, which is less than 5, so you round down: the tens digit stays 8 and the ones digit becomes 0.
What happens when the ones digit is exactly 5?
When the ones digit is exactly 5, round up to the next ten. So 75 rounds to 80, and 35 rounds to 40.
When do 4th graders learn rounding to the nearest ten?
In Saxon Math Intermediate 4, Chapter 2, Lessons 11-20, rounding to the nearest ten is introduced as a key estimation strategy.
How does rounding help with mental math and estimation?
Rounding replaces exact numbers with nearby round numbers that are easier to add, subtract, or multiply mentally. This makes it quick to estimate answers before computing, helping students check if their exact answers are reasonable.