Question 218143
Let  k=# kids  tickets, s=#senior  tickets,,,and  a=# adult  tickets
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k+s+a=91,,,,but  k=2s
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2s +s +a =91
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3s +a =91,,,,,or  a = (91-3s)
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$2*k + $3*s +$5*a =311
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2*(2s) + 3*s +$5*(91-3s) =311,,,,,lots  of  substitutions
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4s +3s -15s +455 =311
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-8s = -144
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s=18
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subst  back  in,,,k=2s = 2*18 =36,,,,a= 91-3s=91-3*18= 37
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Total  #  tickets  = k+s+a=36+18+37=91,,,,,ok
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checking $,,,2*36 +3*18 +5*37 = 72+54+185 = 311,,,,ok