<p>A girl rides her bicycle to school at an average speed of 8 mph. She returns to her house using the same
route at an average speed of 12 mph. If the round trip took 1 hour, how many miles is the round trip.
A. 8
B. 9 3/5
C. 10
D. 11 1/5
E. 12</p>
<p>Time = distance / speed</p>
<p>then</p>
<p>T1 + T2 = Total time (in hours)
(d / 8) + (d / 12) = 1
d = 24 / 5 = distance for 1 trip</p>
<p>Round trip would be 2 * d which is 9 3/5</p>
<p>The answer is always slightly lower than the average of the two</p>
<p>speed=distance/time => time=distance/speed
total time = 1 hour
let distance for one trip be d
then, (d/12 + d/8) = 1
=> 20d = 96 => d = 4.8
Thus, total distance = 4.8 x 2 = 9.6 = 9 3/5</p>