The distanve between Delhi to Agra is \( 200 km \). A train travels the first \( 100 km \) at a speed of \( 50 km / hr \). How fast must the train travel the next \( 100 km \), so as to ayerage \( 70 km / n ^{r} \) fro the chele journey?

Question

The distanve between Delhi to Agra is 200 km. a train travels the first 100 km at a speed of 50 km per hour. how fast must the train travel the next 100 km, so as the average 70km per hour for the whole journey

Answer 1

Time taken to travel first half distance = 100/ 50 = 2 hrs
Time is taken to travel second half distance = 100/v
Average speed = 200/ (2 + 100/v)
70 = 200/ (2 + 100/v)
2 + 100/v = 20/7
100/v = 20/7 – 2 = 6/7
v = 100 * 7/6 Km/h
v = 700/6 km/h