Question

all of 120 km track A train travels the first 30 km at a uniform speed of 30 kilometre per hour how fast must the train travel the next 90 km so as the average speed 60 km per hour for the entire trip

Answer 1

Solution:-
We know that,
$average \: speed = \frac{total \: distance}{total \: time \:}$
$60 = \frac{120}{time}$
$time = \frac{120}{60} \\ = > 2hrs$
Now,
Distance travelled first time =30km
Speed=30km/h
So,
$time = \frac{distance}{speed}$
$time = \frac{30}{30} \\ = > 1hrs$
Then,
Distance travelled second time=90km
Let the speed be x.
So,
$time = \frac{90}{x}$
A/q
$2 = 1 + \frac{90}{x} \\ 2 - 1 = \frac{90}{x} \\ 1 = \frac{90}{x}$
$x = 90$
Hence,he must travel next 90km at average speed of 90km/s so that average speed be 60km/h.