Tom have 100 geese and cows on his far. All in total there are 340 legs. How many geese and how many cows are there.

Answer 1

g + c = 100
2g + 4c = 340
or g + 2c = 170
subtract them ....
c = 70
thus g = 30

check my answer. I obviously have 100 animals, but do
I have 340 legs?

Answer 2

There are X geese and Y cows.
Eq1: x + y = 100.
Eq2: 2x + 4y = 340 Legs.
Multiply Eq1 by -2 and add the Eqs:
-2x - 2y = -200
2x + 4y = 340
Sum: 2y = 140
Y = 70 Cows.
In Eq1, replace Y with 70 and solve for X.