A cyclist rides a bicycle over a route which is 1/3 uphill, 1/3 level, and 1/3 downhill. If the cyclist covers the uphill part of the route at the rate of 12 km per hour and the level part at the rate of 18 km per hour, what rate in km per hour would the cyclist have to travel the downhill part of the route in order to average 18 km per hour for the entire route? Pick:
A) 24 B) 30 C) 36 D) 42 E) 48
Let V be the speed on the downhill section.   Let D be the distance of each of the three equal sections.   Total time T = T1+T2+T3 and 3D/T = 18 km/hour   3D / (D/12 + D/18 + D/V) = 18   1/6 = 1/12 + 1/18 + 1/V   1/V = 1/36 and so V = 36 km/h   The answer is 36.
<result>C</result>
A cyclist rides a bicycle over a route which is 1/3 uphill, 1/3 level, and 1/3 downhill. If the cyclist covers the uphill part of the route at the rate of 12 km per hour and the level part at the rate of 18 km per hour, what rate in km per hour would the cyclist have to travel the downhill part of the route in order to average 18 km per hour for the entire route?