There are 14 bicycles and tricycles in a bicycle shop. Each bicycle has 2 wheels and each tricycle has 3 wheels. There are 37 wheels in all. How many bicycles are there?
B = # of bicycles
T = # of tricycles
2B+3T=37
B+T=14
If we make T=14-B, then we can substitute that into the first equation to find B:
2B+3(14-B)=37
2B+42-3B=37
-B+42=37
-B=-5
B=5
So there are 5 bicycles (along with 9 tricycles).