Answer:
1 km in 15 min
Step-by-step explanation:
You want to know the walking time and distance if the walking speed is 4 km/h, and walking and running at 5 m/s combined to cover 2.5 km in 20 min.
Various units of time, distance, and speed are used here. We choose to convert all to km and hours.
Let x represent the walking time in hours. The total time involved is 20 minutes = 1/3 hour. Then the running time in hours is (1/3 -x). The running speed in km/h is ...
(5 m/s)·(3600 s/h)·(1 km/(1000 m)) = 18 km/h
The total distance in km covered is ...
distance = speed × time
2.5 = (4 )(x) +(18)(1/3 -x)
2.5 = 4x +6 -18x . . . . . . eliminate parentheses
14x = 3.5 . . . . . . . . . . add 14x -2.5
x = 3.5/14 = 1/4 . . . . hour (1/4 hour = 15 minutes)
The walking distance was ...
(4 km/h)(1/4 h) = 1 km
The thief walked 1 km in 15 minutes before he saw the policeman.
