Old McDonald has cows and chickens on his farm. If the animals on his farm have a total of 197 heads and 634 legs, how many cows does Old McDonald have?

Question

Note: A cow has 1 head and 4 legs. A chicken has 1 head and 2 legs.

Answer 1

number of cows = x
number of chickens = y
x+y = 197

4x + 2y = 634 or 2x + y = 317

subtract 2nd - 1st:
x = 120

back into the first:
120+y = 197
y = 77

120 cows and 77 chickens