This is a GMAT joke.
Well not realy a joke but a very hard CR segment, I'm the first to admit it's not that funny, but after a while on the GMAT your brain turns into mash !
"How do you know when to use much or many in quantities ?
If you can't count it, you use much - 1 money, 2 money, 3 money - see doesn't work.
But 1 orange, 2 orange, 3 orange, works fine, then you use many.
So - you should say many Mississippi !!!
How come ? 1 Mississippi, 2 Mississippi, 3 Mississippi !!!" - see works fine !