An aeroplane flies around a square field ABCD of each side 1000 km. Its speed along AB is `250 kmh^(-1)`, along BC `500 kmh^(-1)`, along CD `200 kmh^(-1)`, and along DA `100 kmh^(-1)`. Its average speed (in `kmh^(-1)`) over the entire trip is

Options

A. 225.5
B. 175.5
C. 125.5
D. 190.5

Answer

D

Explanation

Time along the AB `= (1000)/(250) = 4h`
Time along the BC = `(1000)/(500) = 2h`
Time along the CD = `(1000)/(200) = 5h`
Time along the CD `= (1000)/(100) =10 h`
Average speed `= ("Total distance")/("Total time")`
`= (4 xx 1000)/(4 + 2+5+10) = (4000)/(21)`
`= 190.5 km//h`