Question 476566
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I thought you might enjoy comparing Greenestamps' solution to this problem: 

Mrs. Jones has 35 animals, all sheep and ducks, on her farm. The animals 
have a total of 100 legs and 35 heads.  How many sheep and how many ducks
are on her farm?

(1) If all 35 animals were ducks, the total number of legs would be only 
    35*2 = 70, which is 30 legs less than the actual total of 100 legs.
    So we need another 30 legs.
(2) Each sheep has 2 more legs than each duck.
(3) To get the additional 30 legs, the number of sheep needed is 30/2 = 15.
(4) So there are 15 sheep and 35-15 = 20 ducks.

ANSWER: 15 sheep and 20 ducks.

CHECK: 15(4) + 20(2) = 60+40 = 100

Edwin</pre>