Each of the three people individually can complete a certain job in 4, 6, and 8 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?  Choose one.
A) 3 / 8  B) 5 / 12  C) 7 / 24  D) 11 / 36  E) 13 / 48

Rationale: "the two slowest people work at rates of 1 / 6 and 1 / 8 of the job per hour . the sum of these rates is 1 / 6 + 1 / 8 = 7 / 24 of the job per hour . the answer is c ."
Answer: C