As a rule, nouns which are compounded of a participle and a noun use the hyphen; as,
talking-machine, driving-wheel
When fractions are written out, the hyphen is used; as,
one-third, three-fifths
In other numerals expressing a compound number the hyphen is also used; as,
twenty-one, sixty-six
Exercise 196
Punctuate the following letters, supplying a heading and an introduction for each:
1
Gentlemen: