A car covers 4 successive 3 km stretches at speed of 10 kmph, 20 kmph, 30 kmph & 60 kmph resp. Its average speed is  Choose one.
A) 20 kmph B) 40 kmph C) 10 kmph D) 60 kmph E) 80 kmph
20 kmph   20 kmph   20 kmphverage speed = total distance / total time   total distance = 4 * 3= 
<gadget id="calculator">4 * 3</gadget>
<output>12</output>
12 km   total time= 3/10 + 3/20 + 3/30 + 3/60   = 36/60 hr   speed =12/36 * 60= 
<gadget id="calculator">12/36 * 60</gadget>
<output>20</output>
20 kmph
<result>A</result>
A car covers 4 successive 3 km stretches at speed of 10 kmph, 20 kmph, 30 kmph & 60 kmph resp. Its average speed is