SOLUTION: Old McDoNALD had a total of 50 chickens and pigs. Out of curiosity, he counted the total number of legs and arrived at 140. How many pigs does he have?

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Question 963835: Old McDoNALD had a total of 50 chickens and pigs. Out of curiosity, he counted the total number of legs and arrived at 140. How many pigs does he have?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +p+ = number of pigs
Let +c+ = number of chickens
------------------------------
(1) +p+%2B+c+=+50+
(2) +4p+%2B+2c+=+140+
-------------------------
(2) +2p+%2B+c+=+70+
Subtract (1) from (2)
(2) +2p+%2B+c+=+70+
(1) +-p+-+c+=+-50+
--------------------
+p+=+20+
He has 20 pigs
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check:
(1) +20+%2B+c+=+50+
(1) +c+=+30+
and
(2) +2p+%2B+c+=+70+
(2) +2%2A20+%2B+30+=+70+
(2) +40+%2B+30+=+70+
(2) +70+=+70+
OK