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Calculating when your period is going to be to plan for future vacations.
Bob: Hey, let's go camping for Labor Day weekend.
Katie: hmmm, hang on let me look at the calendar. *counting weeks*
Bob: what are you doing?
Katie: Rag math! Gotta make sure Aunt Flo won't be visiting before I agree to the trip.
by Biggins McGee August 31, 2016
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