given: courier travelled in 3 legs without stop
1st leg- avg speed 40km/h
2nd leg- avg speed 60 km/h
3rd leg- avg speed 80 km/h
We have to find if we can find courier's average speed for entire trip?
Lets check both statement one by one.
Statement-1: Ratio of times courier spent on 1st, 2nd and 3rd leg are 3:2:1
Say total time is t
then, 1st leg time is 3/6(t) ; distance travelled for 1st leg=3/6(t)* 40= 20t
2nd leg time is 2/6(t) ; distance travelled for 2nd leg= 2/6(t)*60= 20t
3rd leg time is 1/6(t) ; distance travelled for 3rd leg= 1/6(t)*80= 40/3(t)
total distance travelled = 20t+20t+ 40/3(t)= 160/3(t)
Average speed foe entire trip = total distance travelled/ total time taken = 160/3(t)/t= 160/3 km/h
Statement found sufficient
Statement-2: Ratio of lengths of first, 2nd and 3rd leg are 3:3:2
lets assume total distance as d.
distance for 1st leg= 3/8(d) ; time for 1st leg = (3/8)*(d)/40 = (3/320)*(d)
distance for 2nd leg= 3/8(d) ; time for 2nd leg= (3/8)* (d)/60 = (1/160)*(d)
distance for 3rd leg= 2/8(d) ; time for 3rd leg= (2/8)*(d)/80 = (1/320)*(d)
total time taken = (3/320)*(d)+ (1/160)*(d)+ (1/320)*(d)= (6/320)*(d)
average speed for entire journey= total distance travelled/total time taken= d/(6/320)*(d)= 320/6= 160/3 km/h
Statement-2 is also sufficient
so each statement alone seems sufficient.
My answer choice is -D