An airplane flies along the four sides of a square field at the speeds of 200, 400, 600 and 800 km/h. The average speed of the plane around the field in km/h is Choices:
A) 384 B) 400 C) 500 D) 284 E) None of these
Explanation :   Let each side of the square field be x km.   So, average speed of the plane   = 4x/((x/800)+(x/600)+(x/400)+(x/200))   = (4*2400)/(3+4+6+12) = 9600/25= 
<gadget id="calculator">9600/25</gadget>
<output>384</output>
384   384nswer : 384
<result>A</result>
An airplane flies along the four sides of a square field at the speeds of 200, 400, 600 and 800 km/h. The average speed of the plane around the field in km/h is