Question 385145
 This coming summer, we are meeting up with some family members at Family Fiesta Amusement Park. The ticket price for children is $17 and for adults the ticket price is $31. The total price for all 20 of us to enter the park is $438. 
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People Eq.::: a + c = 20
Value Eq.:: 31a+17c = 438
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Multiply thru People Eq. by 31 to get:
31a + 31c = 31*20
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Subtract from the Value Eq and solve for "c":
-14c = 438-31*20
-14c = -182
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c = 13 (# of child tickets sold)
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Since a + c = 20, a = 7 (# of adult tickets sold)
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Cheers,
Stan H.