Question 395606
A boy spend 765 on 21 tickets
sitting was 45
standing 25
how many times did he buy a ticket to stand. 
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Equations:
Quantity Eq.:::: x + y = 21 tickets
Value Eq.:::::: 45x+25y = 765
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Multiply thru the Quantity Eq. by 45 to get:
45x + 45y = 45*21
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Subtract that from the Value Eq. and solve for "y":
-20y = -180
y = 9 (# of standing tickets sold)
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Cheers,
Stan H.