Question 142563
Dorian and Dingo have a petting zoo with 12 animals, and all of them are either sheep or goats.  They have twice as many sheep as goats.  How many goats do they have? 
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Let # of goats be "x"; Let # of sheep by "y"
EQUATIONS:
x + y = 12
y-2x = 0
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Solve by substitution:
y = 2x 
x + 2x = 12
3x = 12
x = 4 (# of goats)
y = 8 (# of sheep)
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Cheers,
Stan H.