Question
There were 3 times as many boys as girls in the gymnasium at first. After 4 boys left and 7 girls entered the gymnasium, there were 7 more boys than girls remaining in the gymnasium. What was the number of boys in the gymnasium at first?
4 m

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There were 3 times as many boys as girls in the gymnasium at first. After 4 boys left and 7 girls entered the gymnasium, there were 7 more boys than girls remaining in the gymnasium. What was the number of boys in the gymnasium at first?