John started from A to B and Vinod from B to A. If the distance betweeen A and B is 125 km and they meet at 75 km from A, what is the ratio of John's speed to that of Vinod's speed?

New speed = 6/7 of usual speed
Now, time taken = 7/6 of usual time
(7/6 of the usual time) - (usual time) = 10 min
? 1/6 of the usual time = 10 min
? Usual time = 60 min

Let L km distance be covered in T h. So, speed in first case = L/T km/h.
And speed in second case = (L/2)/2T = L/4T km/h
? Required ratio = L/T : L/4T =1 : 1/4 = 4 : 1

Total distance = 30 + 40 = 70 km
Total time taken = (30/6) + 5 = 10 h
? Required average speed = 70/10 = 7 km/h

We know that speed is inversely proportional to time.
Given that, (Speed of A ) : (speed of B ) = 2 : 7
?(Time taken by A ) : (Time taken by B ) = 1/2 : 1/7 = 7 : 2

We know that, speed = Distance / Time
Speed = 12/90 km/min

? Distance covered in 3 h = Speed x Time
= (12/90) x (3 x 60) = 24km

Average speed = 2AB/(A + B)
= 2 x 5 x 3/(5 + 3)
= 30/8
= 3.75 km/h

Distance= Speed x Time = 96 x (100/60) = 160 km
New time = 80/60 h = 4/3 h
New speed = 160 x 3/4 = 40 x 3 =120 km/h

Required average speed = 75 x {(100 - 40)/100} x {(100 + 50)/100}
= 75 x 3/5 x 3/2
= 67.5 km/h

Let the actual speed of train be x and actual time taken be y

Then new speed of train = 5x/6

Therefore, new time taken = 6y/5 (as distance is same in both case)

Given, 6y/5 - y = 1/6 hr , therefore actual time = 50 min

Speed in cm/minute = (Speed in km/hr x 1000 x100 )/60
= 47.52x(50/3)
=79200 cm/min

And Circumference of circle = 2?r
=2 x ( 22 / 7 ) x 21
=132

No. of revolutions = ( Speed in cm/minute ) / circumference of circle in cm
=79200 / 132
=600 rpm