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The number of people is:

 63 - 17 + 19 = 65 (people)

            Answer: 65 people

(toán tính ngược) 

cho hay nhất nhe!!

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Let `x` be the number of people on the train`.`

`*19` people get off`, 17` people get on`.` Now`,` there are `63` people on the train.`.`

`=>x-19+17=63`

`=>x-(19-17)=63`

`=>x-2=63`

`=>x=63+2`

`=>x=65`

So`,` there were `65` people on the train to begin with.