Question

A man on tour travels first 160 km at 64 km/hr and the next 160 km at 80 km/hr. The average speed for the first 320 km of the tour is:

Answer 1

Total time taken =( 160/64 + 160/80 )= 9/2 hrs
average speed = 320 * 2/9 = 71.11 km/hr

Answer 2

d1= 160km s1=64km/hr
t1= d1/s1
t1= 160/64= 10/4hr=2.5 hr

d2=160km
s2=80km/hr
t2= 160/80=2hr

total d=320km
total t= 2+2.5=4.5hr
av.speed= total d/total t
= 320/4.5= 3200/45
= 71.11 km/hr