A and B go cycling in the same direction with speeds of 6 km/hr and 12 km/hr. A car from behind passes them in 9 and 10 seconds respectively. What is the speed of the car?  Choose the correct choice from the following:
A) 96 km/hr
B) 66 km/hr
C) 68 km/hr
D) 26 km/hr
E) 46 km/hr
The relative speed of A and B is 6 km/hr = 1.67 m/s   As the car passes A after 10s, the distance between A and B after 10s (i.e. at 11th second) is the distance covered by car in 1 second.   Therefore, at t = 11, d = 1.67 * 11   d = 18.33 m   v = d/t = 18.33/1= 
<gadget id="calculator">18.33/1</gadget>
<output>18.33</output>
18.33m/s   v= 66 km/hr   ANSWER: 66 km/hr
<result>B</result>
A and B go cycling in the same direction with speeds of 6 km/hr and 12 km/hr. A car from behind passes them in 9 and 10 seconds respectively. What is the speed of the car?