Numbers

Q. In the admittedly rare circumstances when you want to write out the name of a large number, are there any agreed-upon guidelines for the usage of the word “and”? Is it “six hundred seventy-two” or “six hundred and seventy-two”? I was taught the former in grade school; a colleague was taught the latter, equally adamantly. I should note that said colleague is Canadian; is this perhaps a question of American versus British usage? All consulted manuals are, inexplicably, silent on the matter.

A. See paragraph 9.5 in the sixteenth edition of The Chicago Manual of Style. Some writers prefer using and, but Chicago’s preference is to omit it.