Answer:
The Man needs to run at 9 mph
Step-by-step explanation:
Let M stand for the man's speed in mph. When the man
runs toward point A, the relative speed of the train with respect
to the man is the train's speed plus the man's speed (45 + M).
When he runs toward point B, the relative speed of the train is the
train's speed minus the man's speed (45 - M).
When he runs toward the train the distance he covers is 2 units.
When he runs in the direction of the train the distance he covers
is 3 units. We can now write that the ratio of the relative speed
of the train when he is running toward point A to the relative speed
of the train when he is running toward point B, is equal to the
inverse ratio of the two distance units or
(45 + M) 3
----------- = ---
(45 - M) 2
90+2 M=135-3 M
⇒5 M = 45
⇒ M = 9 mph
The Man needs to run at 9 mph
