Q. I am taking a college course in copyediting. My professor and I were having a discussion and I would like to know who is correct. We were presented with this sentence for correction: Of the 400 members, about 300 were over 60 years old, but at least 50 were under the age of 30. I understand the rules stated in CMOS 9.2 and 9.4 would apply here and require all of the numbers to be spelled out. However, I chose to leave the 60 and 30 in numerical form in accordance with 9.7, which says that an exception can be made “to avoid a thickly clustered group of spelled-out numbers.” There are no guidelines that state when to apply the exception, nor are there examples to lead me to a definitive answer. Help please. How do you decide?

A. Your editing would make it easier for some readers to take in the numbers, while others would be distracted by a perceived inconsistency. That is a fundamental challenge for editors. You decide based on how consistent the text is to begin with, how much work it will be to carry out a change throughout a document, and how likely it is that you’ll end up introducing inconsistencies. You weigh the work and the dangers against what you think most readers will find helpful. There’s usually no “correct” winner; it’s a judgment call.