In a yard there are ducks and cows If there are 35 heads and 110 legs. How many ducks are there?

Well, well, well, looks like we've got a little math puzzle on our hands. If we let D be the number of ducks and C be the number of cows, we have the lovely equations D + C = 35 and 2D + 4C = 110. Solving this system of equations, we find that there are 15 ducks waddling around causing a ruckus in the yard.