Question 1174418
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<pre>

Let x be the number of cows.

Then the number of chickens is 2x, according to the condition.


Counting the legs, you have this equation


    4x + 2*(2x) = 640,   or


    4x + 4x = 640

      8x    = 640

       x    = 640/8 = 80.


<U>ANSWER</U>.  80 cows.
</pre>

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