At billy‘s preschool they have bicycles and tricycles with a total of 57 wheels. the number of bicycles is three less than three times the number of tricycles. how many of each are there?

Use b for bicycles b and t for tricycles.

We know that each bicycle has 2 wheels, and each tricycle has 3 wheels, and if the entire number of wheels is 57, that means the 

equation would be: 2b + 3t = 57

We can "separate" b by calling it "25 - t" as an alternative, 

2(25 - t) + 3t = 57, or

50 - 2t + 3t = 57,

or 50 + t = 57, so

t = 7 So there must be 18 bicycles and 7 tricycles.

CHECKING:You can check this out by multiplying 7 tricycles x 3 wheels, which is 21,

and 18 bicycles x 2 wheels, which is 36

36 + 21 = 57