Triathlete Dan runs along a 2-mile stretch of river and then swims back along the same route. If Dan runs at a rate of 10 miles per hour and swims at a rate of 5 miles per hour, what is his average rate for the entire trip in miles per minute?
Options
A) 1 / 9
B) 2 / 15
C) 3 / 15
D) 1 / 4
E) 3 / 8

Rationale: dan travels 4 miles round trip . running part : ( 2 / 10 = 1 / 5 * 60 = 12 minutes ) swimming part : ( 2 / 5 = 2 / 5 * 60 = 24 minutes ) 4 miles in ( 12 + 24 ) minutes 4 / 36 = 1 / 9 mile per minute answer : 1 / 9 mile per minute
Answer: A