Reading Math
Two-digit numbers between 21 and 99 that do not end in zero are written in words with a hyphen connecting the tens word and the ones word. For example, 51 is 'fifty-one' and 87 is 'eighty-seven.' This rule, covered in Chapter 1 of Saxon Math Intermediate 4, ensures consistency when writing numbers as words—a skill needed for check writing, reading prices, and translating number-word problems in math.
Key Concepts
Property The names of two digit numbers greater than twenty that do not end in zero are written with a hyphen.
Example The number 51 is written as 'fifty one'. The number 87 is written as 'eighty seven'. The number 33 is written as 'thirty three'.
Explanation When you write out two digit numbers in words, think of the hyphen as a special connector that holds the words together. For any number from twenty one to ninety nine (as long as it doesn't end in zero), you need this little dash to properly link the tens part and the ones part, like making 'seventy' and 'four' become 'seventy four'.
Common Questions
How do you write two-digit numbers in words?
Write the tens part, then a hyphen, then the ones part. For example, 34 = 'thirty-four,' 67 = 'sixty-seven,' 89 = 'eighty-nine.'
Which two-digit numbers do NOT use a hyphen?
Numbers ending in zero do not use a hyphen: 20 = 'twenty,' 50 = 'fifty,' 90 = 'ninety.' Also, 10–19 have unique names (ten, eleven, twelve, thirteen, etc.) without hyphens.
When do Grade 4 students learn the hyphen rule for numbers in words?
This rule is introduced in Chapter 1 of Saxon Math Intermediate 4 as students refine their number vocabulary and reading fluency.
Why are hyphens used in number words?
Hyphens show that the two words together name one number. 'Thirty four' (no hyphen) could be misread as 30 + 4 as two separate numbers; 'thirty-four' is clearly one value.
How does this rule affect writing numbers in word problems?
Word problems sometimes give numbers in words. Recognizing 'forty-six' as 46 or 'ninety-nine' as 99 quickly is essential for setting up equations correctly.
Does the hyphen rule apply to numbers above 99?
Yes, for the two-digit parts within larger numbers. 'Two hundred thirty-seven' has a hyphen in 'thirty-seven' but not around the word 'hundred.'