Let the usual speed of the train be .
Reduced speed of the train
Total distance to be covered
Time taken by the train to cover the distance at usual speed Time
Time taken by the train to cover the distance at reduced speed
According to the given condition,
Time taken by the train to cover the distance at reduced speed = Time taken by the train to cover the distance at usual speed
or
or
(Speed cannot be negative)
Hence, the usual speed of the train is .