Question 757534
let it take t hr to complete the second part i.e. 70 kms of its journey
so the total length of the journey=50+70=120 km
& total time=90/60+t=1.5+t hr
so the average speed=120/(1.5+t)
but 120/(1.5+t)=50
or 1.5+t=120/50=2.4
or t=2.4-1.5=0.9hr=54 mins