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
A08
May 29, 2018

Given #d_1:d_2::2:1#
#d_1/d_2=2/1#
Let #k# be common factor.

#=>d_1=2k#
and #d_2=k#

Total distance covered #d=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#

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