1.

Abdul, while driving to school, computes the average speed for his trip to be 20 km h^(-1). On his return trip along the same route, there is less traffic and the average speed is 30 km h^(-1). What is the average speed for Abdul's trip?

Answer»

Solution :Let the DISTANCE of school be x km from house of Abdul.
While driving to school,
Average speed `= ("Distance")/("Time")`
`therefore` Time `= ("Distance")/("Average speed")`
`= (x km)/(20 km h ^(-1))`
`= (x)/(20) h ""…(1)`
On return TRIP,
Average speed `= ("Distance")/("Time")`
`therefore` Time `= ("Distance")/("Average speed")`
`= (xkm)/(30 km h ^(-1))` |
`= (x)/(30) h ""...(2)`
Total distance `= (x + x) km = 2 xkm.`
Total time `= ((x )/(20) + (x)/(30)) h `
`= (3X + 2x )/( 60) h`
`= (5x)/(60) h = (x)/(12) h`
Average speed `= ("Total distance")/("Total time")`
`= (2x km)/(x//12 h)`
`= (2x)/(x) XX 12 km h ^(-1) = 24 km h ^(-1)`
The average speed for Abdul.s trip is `24 km h ^(-1).`


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