Question

On a 100 km track a train travels the first 30 km at a uniform speed of 30km/h. How fast must the train travel the next 70 km so as to average 40km/h for the entire trip

Answer 1

let time for rest of the journey be x
V avg = total distance / total time
=100/x+1=40
so speed is 70/1.5 km /h

Answer 2

let averege speed be x.
2nd speeds be y.
$x = (2 \times 30 \times y) \div 30 + y$
since x=40
40=(60y)/30+y
40×(30+y)=60y
1200+40y=60y
1200=20y
y=60kmph
hope helped☺☺☺☺☺☺☺‍
for further enquiry comment.