Question 432431
There are 200 heads on a farm and 540 feet.
How many cows (4 legs) and how many chickens (2 legs) are there?
<pre>
Two ways to do it. In your head and by algebra.

In your head:
540 feet means 270 pairs of feet, 200 of which are pairs of front feet,
since all animals have 1 head and 1 pair of front feet.  The remaining 70
pairs of feet are pairs of hind feet, which belong to the 70 cows, so the
other 130 animals are chickens.

By algebra:
x = number of cows
y = number of chickens

 x +  y = 200
4x + 2y = 540

Multiply the top equation by -2

-2x - 2y = -400
 4x + 2y = 540
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 2x      = 140
       x = 70  

 x + y = 200
70 + y = 200
     y = 130.

Edwin</pre>