A person travels the total distance in two parts in ratio 2:1 with a constant speed of 30km/h in the first part and 40km/h in the second part.What is average speed of the journey?

1 Answer
May 29, 2018

Given d_1:d_2::2:1d1:d2::2:1
d_1/d_2=2/1d1d2=21
Let kk be common factor.

=>d_1=2kd1=2k
and d_2=kd2=k

Total distance covered d=2k+k=3kd=2k+k=3k

Time taken to perform first part t_1=d_1/v_1=(2k)/30=k/15\ h
Time taken to perform second part t_2=d_2/v_2=(k)/40\ h
Total time taken for journey t=k/15+k/40=k(8+3)/120=(11k)/120

"Average speed"="Total distance"/"Total time taken"
=>"Average speed"=(3k)/((11k)/120)
=>"Average speed"=(3xx120)/(11)=32.bar72\ bb(kmh)^-1