Question

assume the distance between city A and city B is 800km a person travel between city A and city B at the speed of 90km per hour and he return back to city A at the uniform speed of 60km per hour determine the average speed of the total journey​

Answer 1

avg speed =800/90)+800/60

Answer 2

Solution :-

→ Distance covered = 800 km

→ Speed from city A to city B = 90km/h

so,

→ Time taken = 800/90 = 80/9 hours.

now,

→ Distance covered = 800 km

→ Speed from city B to city A = 60km/h

so,

→ Time taken = 800/60 = 40/3 hours.

then,

→ Total distance covered = 800 + 800 = 1600 km

→ Total time taken = 80/9 + 40/3 = (80 + 120)/9 = 200/9 hours .

therefore,

→ Average speed = Total distance covered / Total time taken = 1600/(200/9) = 1600 * (9/200) = 72 km/h (Ans.)

Direct formula :-

• 2 * S1 * S2 / (S1 + S2)

→ S1 = first speed = 90km/h

→ S2 = second speed = 60 km/h

then,

→ Average speed = 2 * 90 * 60 / (90 + 60) = 10800 / 150 = 72 km/h (Ans.)

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