Many agents ask for the first 3 chapters, or 30 pages. My chapters are very short - the first 3 are 13 pages. Can I send 30 pages if they ask for the first 3 chapters? Simple question, but world of difference in numbers here.
Absent the phrase "whichever is more" or "whichever is fewer" I'd send the more. In your case 30 pages.
Here's why: way too many times what the author sends as the first ten pages is the writing equivilent of throat clearing or orchestral tuning. Warm up. If all I've got are those ten pages I can't flip ahead and see where the story really starts. (Of course I'm sure that's not the case with YOUR book, right?)
Even if I'm not going to take your project (sad lack of taste on my part obviously) I can at least tell you that I think the story starts on page 11, or 12, or 30.
The other thing is: there's no such thing as the query police (sadly) and so no one is going to arrest you for sending 30 pages instead of stopping at 13.
Just remember to embed them in the email UNLESS the agent says otherwise. I am seeing a couple agents that are asking for attachments but that is NOT the norm.
And if an agent DOES reject you for sending 30 pages instead of 13, frankly, you might not think so now, but you're better off. Holy moly, that kind of strait jacket glued to the rules approach is bad bad bad for what you need in an agent these days.