Rounding Numbers: Tens and Hundreds

What You'll Learn

• Rounding means finding a nearby number that is easier to work with
• To round to the nearest ten, look at the ones digit
• If the ones digit is 5 or more, round UP to the next ten (36 -> 40)
• If the ones digit is 4 or less, round DOWN to the current ten (33 -> 30)
• To round to the nearest hundred, look at the tens digit
• If the tens digit is 5 or more, round UP to the next hundred (267 -> 300)
• If the tens digit is 4 or less, round DOWN to the current hundred (133 -> 100)
• The magic rule: 5 or more, let it soar; 4 or less, let it rest

Words to Know

Round

To change a number to a nearby ten or hundred that is easier to work with

"36 rounds to 40."

Nearest ten

The closest multiple of 10

"The nearest ten to 36 is 40."

Nearest hundred

The closest multiple of 100

"The nearest hundred to 267 is 300."

Digit

A single number from 0 to 9

"In 267, the tens digit is 6."

Estimate

A good guess using rounding

"I estimate 48 + 31 is about 80."

Check What You Learned

Fun Facts

• Rounding means replacing a number with an approximate value that is easier to work with

  Source: CCSS / math textbooks

• To round to the nearest ten, look at the ones digit: 5 or more rounds up, 4 or less rounds down

  Source: CCSS.MATH.CONTENT.3.NBT.A.1

• 36 rounded to the nearest ten is 40 because the ones digit (6) is 5 or more

  Source: math textbooks

• 33 rounded to the nearest ten is 30 because the ones digit (3) is 4 or less

  Source: math textbooks

• To round to the nearest hundred, look at the tens digit: 5 or more rounds up, 4 or less rounds down

  Source: CCSS.MATH.CONTENT.3.NBT.A.1

• 267 rounded to the nearest hundred is 300 because the tens digit (6) is 5 or more

  Source: math textbooks