yes,but your chain maybe too long and your front derailer will need to be adjusted.Maybe even replaced.
I'm no expert,so here is my explanation of the gears.
The rear gears(freewheel/cassette) can have 1 to 10 gears on it.this multiplied by the crank gears(chain rings) equals the speed of your bike.ex.3 rings in front 7 in back is a 21 speed. 2 in front 5 in back is a ten speed.
You should really check out Sheldon Brown's articles I've learned a lot. http://sheldonbrown.com/articles.html
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