Question 1199615
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At the movie theatre, child admission is $6.60 and adult admission is 9.70On Monday, three times as many adult tickets as child tickets were sold, for a total sales of $1320.90How many child tickets were sold that day? 

Let number of child tickets sold be C
Then number of adult tickets sold = 3C
We then get the following total-sales equation: 6.6C + 9.7(3C) = 1,320.9 
                                                  6.6C + 29.1C = 1,320.9
                                                         35.7C = 1,320.9
                           Number of child tickets sold, or {{{highlight_green(matrix(1,7, C, "=", "1,320.9"/35.7, "=", "13,209"/357, "=", highlight(37)))}}}</pre>