Question

The distance between delhi and agra is 200km. a train travels the first 100 km at a speed of 50 km/h . how fast must the train travel the next 100 km, so as to average 70 km/h for the whole journey?

Answer 1

the formula for avg speed is [v(1)+v(2)]/n .In this case n is 2 as there are 2 speeds .
so the formula becomes (50+x)/2=70
solving it we get 90