Question 1134192
r, tickets at regular rate
d, tickets at discounted rate


{{{system(r=2d-220,850r+400d=590000)}}}

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The question asks for d.
Simplify the revenue equation and substitute for r.  Solve for d.


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{{{17r+8d=11800}}}
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{{{17(2d-220)+8d=11800}}}
{{{34d-3740+8d=11800}}}
{{{42d=11800+3740}}}

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{{{highlight(d=370)}}}