Each of the three people individually can complete a certain job in 3, 4, 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?
Answers:
A) 1/3
B) 9/20
C) 8/15
D) 5/12
E) 2/3
The two slowest people work at rates of 1/4 and 1/6 of the job per hour.   The sum of these rates is 1/4 + 1/6 = 5/12 of the job per hour.   The answer is 5/12.
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Each of the three people individually can complete a certain job in 3, 4, 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?