1.02 Rounding
Rounding
Rounding is a way to simplify our numbers, to help with estimating. With whole numbers, we might round to the nearest ten, or hundred. With decimals, we might round to the nearest unit, tenth or hundredth.
Rounding $13$13 to the nearest ten is the same as asking if $13$13 is closer to $10$10, or closer to $20$20. As we know that $15$15 is halfway between $10$10 and $20$20, and $13$13 is less than halfway, $13$13 must be closer to $10$10.
Rounding $175$175 to the nearest hundred is the same as asking if $175$175 is closer to $100$100 or $200$200. As we know that $150$150 is halfway between $100$100 and $200$200, and $175$175 is greater than $150$150, then $175$175 is closer to $200$200 than $100$100.
It's this notion of "halfway-ness" that leads us to the following rule for rounding.
When rounding, look at the digit in the column to the right of the column you are rounding to. If that digit is $5$5 or more (i.e. halfway or more than halfway to the next $10$10), then round up. If it is less than $5$5, (i.e. less than halfway to the previous $10$10), then round down.
Practice questions
Question 1
Round $54$54 to the nearest ten.
Question 2
Round $370$370 to the nearest hundred.
Question 3
Round $96501$96501 to the nearest thousand.