Bob travels at an average speed of 12km/h, to the school and then return to the home he travels at an average speed of 10km/h. Which of the following is the closest approximation of Bob's average speed, in kilometers per hour, for the trip? Select
A) 6.3 B) 2.9 C) 15.2 D) 10.9 E) 9.1
Since we're not given a distance to work with, we can TEST any distance that we like. Here, since the speeds are 12 km/hour and 10 km/hour, using a multiple of both 12 and 10 would make the math easiest.   Let's set the Distance up the hill at 60 km.   So, going school, we have....   D = (R)(T)   60 = (5)(T)   60/12= 
<gadget id="calculator">60/12</gadget>
<output>5</output>
5= T   5 hours to go school   Going home, we have....   10.9 = (R)(T)   60 = (10)(T)   60/10= 
<gadget id="calculator">60/10</gadget>
<output>6</output>
6= T   6 hours to go home   Total 10.9istance = 120 km   Total Time = 5+6= 
<gadget id="calculator">5+6</gadget>
<output>11</output>
11 hours   Average Speed= 120/11 = 10.9 km/hour   10.9
<result>D</result>
Bob travels at an average speed of 12km/h, to the school and then return to the home he travels at an average speed of 10km/h. Which of the following is the closest approximation of Bob's average speed, in kilometers per hour, for the trip?