Each of the three people individually can complete a certain job in 4, 5, and 6 hours, respectively. What is the lowest fraction of the job that can be done in 1 hour by 2 of the people working together at their respective rates? Select:
A) 4 / 15  B) 7 / 30  C) 11 / 30  D) 5 / 18  E) 7 / 18

Rationale: "the two slowest people work at rates of 1 / 5 and 1 / 6 of the job per hour . the sum of these rates is 1 / 5 + 1 / 6 = 11 / 30 of the job per hour . the answer is c ."
Answer: C