Answer:
68:39
Step-by-step explanation:
We have to find the ratio of the man's running speed to the sidewalk's speed.
Let running speed of man=x
Sidewalk's speed=y
When man running in the same direction as side walk is moving.
Then, total speed=x+y
Time=2.9 s
When a man running in opposite direction as the side walk is moving.
Then, total speed =x-y
Time =10.7 s
Distance traveled in both cases remain same.
Suppose , d is the distance from one end to another end.








Hence, the ratio of the man's running speed to the sidewalk's speed =68:39