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Let x = number of tickets over 100.
==> price of ticket is 12 - 0.10x
==> number of tickets is 100 + x
==> Income, or revenue, is
. Since the the coefficient of
is negative (-0.10), there is an absolute maximum (parabola faces downward). The x-value that gives the maximum income is
. Hence 100 + 10 = 110 tickets must be sold to get maximum income.