Question

Car travels the first third of a distance with the speed of 10 km per hr, the second third at 20 km per hour and the last third at 60 km per hour what is its means speed over the entire distance?

Answer 1

Let the total distance travelled be x km Then total time taken =  

10

x/3

​  

+  

20

x/3

​  

+  

60

x/3

​  

=  

30

x

​  

+  

60

x

​  

+  

180

x

​  

 

=  

180

6x+3x+x

​  

=  

180

10x

​  

=  

18

x

​  

 hrs Then average speed = =  

Totaltimetaken

Totaldistancetravelled

​  

 

=  

x/18

x

​  

 km/hr = 18 km/