Question

a car can average 20km/hour up a hill and 60km/hour down the same hill . what is the average speed for the whole trip?

Answer 1

Average speed=(20×60×2)/(20+60)=30km /h

Answer 2

Answer:

So, average speed is 30km/hr.

Step-by-step explanation:

Let us assume that car covers k km one way.

Now, uphill speed is 20km/hr

So, time taken to reach uphill is k/20 hrs.

Similarly, downhill speed is 60km/hr.

So, time taken to reach downhill is k/60 hr.

So, total distance covered is ( k + k) = 2k km

Total time taken = $\frac{k}{20}  + \frac{k}{60}  = \frac{3k + k}{60}  = \frac{4k}{60}  hr$

So, average speed =  Total Distance / Total time

= $\frac{2k}{\frac{4k}{60} }  = 2k \times\frac{60}{4k}  = 30km/hr$

So, average speed is 30km/hr.