SELECT MAX("speed [km/h (mph)]") - MIN("speed [km/h (mph)]") FROM table_204_821
what is the difference in speed number of the fastest and slowest trains in km/h ?
CREATE TABLE table_204_821 (
    id number,
    "speed [km/h (mph)]" text,
    "train" text,
    "type" text,
    "location" text,
    "date" text,
    "comments" text
)