<PRE><B>Question 1105671</B>
let x be the number of adult tickets and y be the number of children tickets sold, then
:
1) x + y = 200
:
2) 10x + 7y = 1550
:
solve equation 1 for y
:
y = 200 - x
:
substitute for y in equation 2
:
10x +7(200 - x) = 1550
:
10x +1400 -7x = 1550
:
3x = 150
:
x = 50
:
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there were 50 adult tickets sold
: 
check the answer
:
substitute 50 for x and 150 for y in equation 2
:
10*50 + 7*150 = 1550
:
500 + 1050 = 1550
:
1550 = 1550
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