A boy rides his bicycle 10 km at an average speed of 12 km/hr and again travels 12 km at an average speed of 10 km/hr. His average speed for the entire trip is approximately.  Pick one:
A) 10.2 km/hr
B) 10.4 km/hr
C) 10.6 km/hr
D) 10.8 km/hr
E) None of these
Explanation :   Total distance traveled = (10+12)= 
<gadget id="calculator">(10+12)</gadget>
<output>22</output>
22 km   Total time taken= [10/12 + 12/10] hrs = 61/30 hrs   Average speed = [22*30/61] km/hr = 10.8 km/hr.   Answer : 10.8 km/hr
<result>D</result>
A boy rides his bicycle 10 km at an average speed of 12 km/hr and again travels 12 km at an average speed of 10 km/hr. His average speed for the entire trip is approximately.