A man travelled from a school to a park at a speed of 20 km/h and walked back at a speed of 5 km/h. If the whole journey took 5 h, find the distance of the school from the park.

Correct option is D

Given:

Speed from school to park: 20 km/h

Speed from park to school: 5 km/h

Total journey time: 5 hours

Formula Used: 

Time = $$\frac{Distance}{Speed}$$​​

Solution:

Let the distance from the school to the park be d kilometers.

time taken to travel from the school to the park at 20 km/h is 

​$$Time_{to\ park}$$ = $$\frac{d}{20}$$ hours

Time taken to walk back from the park to the school at 5 km/h is

​$$Time_{to\ school}$$ = $$\frac{d}{5}$$ ​hours

The total time for the journey is 5 hours ;

​$$\frac{d}{20}+\frac{d}{5} = 5$$ = $$\frac{d}{20}+\frac{4d}{20} = 5$$ = $$\frac{5d}{20} =5$$

$$\frac{d}{4}$$ = 5

d = 20 

The distance from the school to the park is 20 kilometers

Thus, correct answer (d) 20 km