Math Concepts: Number Words and Rounding

Number Words and Values

• Numbers 21 to 29 are expressed as "two tens plus one", "two tens plus two", etc.
• 30 is "three tens"
• 40 is "four tens"
• 50 is "five tens"
• 60 is "six tens"
• 70 is "seven tens"
• 80 is "eight tens"
• 90 is "nine tens"
• 100 is "one hundred"

Rounding to the Nearest Ten

• To round a number to the nearest ten, look at the ones digit.

• If the ones digit is 5 or greater, round up to the next ten.

• If the ones digit is 4 or less, round down to the previous ten.

• Example: 30 rounds to 30

• Example: 31 rounds to 30

• Example: 35 rounds to 40

• Example: 51 rounds to 50

• Example: 55 rounds to 60

• Example: 72 rounds to 70

• Example: 78 rounds to 80

• Example: 83 rounds to 80

• Example: 94 rounds to 90

• Example: 98 rounds to 100

• Example: 19 rounds to 20

• Example: 26 rounds to 30

• Example: 87 rounds to 90

Place Value

• Example: In number 47, the place value of 7 is units or ones and the place value of 4 is tens
• Example: In number 85, the place value of 5 is units or ones and the place value of 8 is tens