Question 268358
Hello, 
We can set up two equations. Let x be the adult tickets and y for the student tickets. 
5x+2.5y=1375
x+y=400
Now multiply the second equation by -5 to get:
-5x-5y=-2000 Now add this to the other equation:
5x+2.5=1375 This we give us:
-2.5y=-625 Divide both sides by -2.5 to get:
y=250
There we go 250 student tickets were sold. 
You can plug in the answer and see if it works. 
Make sense?
RJ
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www.math-unlock.com