Find the time taken to travel between two cities

Question

At a speed of 40 Kmph^-1 , vehicle takes 6 hours to travel the distance between two cities.

Find the total number of hours it takes to travel the distance between two cities if one half of the distance is traveled at a speed of 30 kmph^-1 and the other half at 20 kmph^-1.

Any Ideas on how to begin ?

Answer 1

See the distance between the cities is $40\times 6=240 km.$ Now it's given that half of the distance is covered with 30kph and remaining with 20kph. So the total time taken is $$ \frac{120}{30}+\frac{120}{20}=10 hrs. $$