Q. I edit math textbooks for American students, and although we have a copy of your fine manual in the office, I need help with a query from a writer. When a number is written in words, do you separate the values with a comma: e.g., four thousand three hundred and twenty-one; or, four thousand, three hundred, and twenty-one? Hope you can help.
A. Although CMOS is silent on spelling out such complex numbers, common sense dictates leaving out the commas, since with commas, one large number could be misread as three numbers: 4,000, 300, and 21. Please note that CMOS leaves out and as well: three hundred twenty-one.