My property prof. said "God I wish they had math on the LSAT" last semester when a student couldn't figure out some basic math for adverse possession. We all thought it was hilarious but the kid it was directed at didn't think so.
Lawyers are supposed to be bad at math just like doctors are supposed to be bad at handwriting. It's the nature of the universe; the way God intended it.
This is evidenced in how lawyers bill. It's always big round easy to multiply and divide numbers for retainers and hourly rates. An attorney retainer will never be a number like $47,863.53 instead of $50k, nor will an hourly billable rate be something like $387.50 instead of a round $400