Question

car travels first half distance between two places with uniform speed of 60 km per second what should be its uniform speed for the second half of the distance of that its average speed over the entire journey becomes 90 km per second per hour

Answer 1

Let the distance be 2d.
& let The time be t.
Also let the speed be s.
Case1:
Distance (1)=d
Speed (1)=60km/h
:.Time(1)=distance(1)/speed(1)
=D/60
Case2:
Distance (2)=d
Speed(2)=s
:. Time (2)=distance (2)/speed(2)
=D/s
Now,
Average speed=total distance/total time
90=(d+d)/{t(1)+t(2)}
2d/(d/60+d/s)
60=2d/(ds+60d)60s
60=(2d×60s)/(ds+60d)
60=120ds/d(s+60)
60/120=s/(s+60)
1/2s=1/s+60
2s=s+60
2s-s=60
s=60
(ÆÑẞWĒR)