Bunuel wrote:
A river boat leaves Silver Town and travels upstream to Gold Town at an average speed of 6 kilometers per hour. It returns by the same route at an average speed of 9 kilometers per hour. What is the average speed for the round-trip in kilometers per hour?
A) 7.0
B) 7.1
C) 7.2
D) 7.5
E) 8.0
A) 7.0
B) 7.1
C) 7.2
D) 7.5
E) 8.0
Average Speed = 2 a * b/ (a+b)
= 2 * 6 * 9 / 15
= 7.2
C