Question 1021840
Let A be the number of adults, B be the number of children, and C be the number of children under 1.
There are multiple solutions based on this information.
{{{A+B+C+120}}} ,-- Total number of people
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{{{20A+10B+5C=1555}}} <--- Total box office receipts
{{{4A+2B+C=311}}}
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{{{C=120-A-B}}}
{{{C=311-4A-2B}}}
{{{120-A-B=311-4A-2B}}}
{{{B=191-3A}}}
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Then substituting,
{{{C=120-A-(191-3A)}}}
{{{C=2A-71}}}
All three numbers must be integers and greater than or equal to zero,
{{{191-3A>0}}}
{{{191>3A}}}
{{{A<191/3}}}
{{{A<=63}}}
and
{{{2A-71>0}}}
{{{2A>71}}}
{{{A>=36}}}
So then,
{{{B=191-3A}}}
{{{C=2A-71}}}
with
{{{36<=A<=63}}}