Use place value understanding to round whole numbers to the nearest 10 or 100.
Official wording from the Common Core State Standards for Mathematics (Β© 2010 National Governors Association Center for Best Practices and Council of Chief State School Officers). View on thecorestandards.org
Rounding is about closeness. To round 347 to the nearest ten, a student asks which two tens it sits between (340 and 350) and which one it is nearer to. Since 347 is 3 away from 350 and 7 away from 340, it rounds to 350. Rounding to the nearest hundred works the same way with hundreds: 347 sits between 300 and 400 and is nearer 300.
Third graders should understand rounding through place value and number lines before they lean on a rule like "5 or more, round up." The halfway point matters: 345 is exactly halfway between 340 and 350, and by convention it rounds up to 350. Rounding is not an end in itself. It powers estimation, which students use in 3.OA.D.8 to check that answers to word problems are sensible, and it helps with mental math such as deciding whether 298 + 413 will be closer to 700 or 800.
When asked to round 462 to the nearest hundred, some students look at the ones digit and write 460. Circle the place being rounded to and look at the digit just to its right.
Students may round 432 to the nearest ten as 420, thinking "round down" means take one away from the tens. Rounding down keeps the tens digit and replaces the ones with zero: 430.
Rounding 349 to the nearest ten (350) and then to the nearest hundred gives 400, but 349 is closer to 300. Always round the original number.
Writing 5 instead of 500 when rounding 487 to the nearest hundred loses the size of the number. The rounded number should still be close to the original.
Round 638 to the nearest ten and to the nearest hundred.
Answer: 638 rounds to 640 (nearest ten) and 600 (nearest hundred).
Use open number lines with only the two benchmark numbers and the midpoint marked. Students place the number, then decide which end is nearer. A hundreds chart or a "rounding hill" picture can help, but make sure students can explain closeness rather than just reciting a rhyme.
Assessment items include rounding to a given place, picking all numbers that round to a given value, and using rounding to estimate in word problems. Questions about numbers that round to the same value ("which numbers round to 300?") are a good test of real understanding.
Original questions written for this standard. Choose an option or type your answer, then press Check. Every question has a worked explanation.
Answer: D) 350
347 is between 340 and 350. It is 3 away from 350 and 7 away from 340, so it rounds to 350.
Answer: 500
462 is between 400 and 500. The halfway point is 450, and 462 is past it, so it rounds to 500.
Answer: 90
85 is exactly halfway between 80 and 90. Numbers exactly halfway round up, so 85 rounds to 90.
Answer: C) 251
251 is between 200 and 300 and past the halfway point 250, so it rounds to 300. 249 rounds to 200, and 351 and 380 round to 400.
Answer: 710
709 is between 700 and 710 and only 1 away from 710, so it rounds to 710.
Answer: A) 300
349 is below the halfway point of 350, so it rounds to 300. Sam rounded to 350 first and then rounded again, which is not allowed.
Understand that the three digits of a three-digit number represent amounts of hundreds, tens, and ones; e.g., 706 equals 7 hundreds, 0 tens, and 6 ones. Understand the following as special cases:
Mentally add 10 or 100 to a given number 100-900, and mentally subtract 10 or 100 from a given number 100-900.
A full lesson with slides, activities and an exit ticket on rounding to the nearest 10 or 100, pitched to grade 3 and editable in PowerPoint or Google Slides.
Make a lesson βA printable, differentiated worksheet on 3.NBT.A.1 with an answer key, ready in about a minute.
Make a worksheet βTurn rounding to the nearest 10 or 100 into a quiz students answer online that marks itself, with a class summary for you.
Build a test βThird graders round whole numbers, usually up to 1,000, to the nearest 10 or 100. Rounding to other places comes in 4.NBT.A.3.
It is exactly halfway between 400 and 500, and the usual convention is to round up, so 450 rounds to 500.