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딸아이가 수학 문제를 물어봅니다... ^^
"아빠… 이 문제 잘 모르겠어요."
"그래… 어떤 문젠데..."
흠… 옛날 생각도 나고, 살짝 긴장도 되는군요... ^^
There is a group of boys and girls waiting for school buses.
25 girls get on the first bus.
The ratio of boys to girls at the stop is now 3 : 2.
15 boys get on the second bus.
There are now the same number of boys and girls at the bus stop.
How many students altogether were originally at the bus stop... ??
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X : Y - 25 = 3 : 2
X - 15 = Y - 25
2X - 3Y = -75
X - Y = -10
X = 45
Y = 55
X + Y = 100
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휴... 다행입니다... ^^