Question
Some passengers boarded the mini-bus at the interchange. At the first stop, 7 passengers alighted and 8 passengers boarded the mini-bus. At the second stop, 3 passengers alighted and another 4 passengers boarded the mini-bus. In the end, there were 10 passengers on the mini-bus. How many passengers boarded the mini-bus at the interchange at first?
4 m

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Some passengers boarded the mini-bus at the interchange. At the first stop, 7 passengers alighted and 8 passengers boarded the mini-bus. At the second stop, 3 passengers alighted and another 4 passengers boarded the mini-bus. In the end, there were 10 passengers on the mini-bus. How many passengers boarded the mini-bus at the interchange at first?