The problem above is the equivalent of the following:
Adam can complete a certain job in 14 minutes. Bob can complete this same job in 14 seconds. If Adam and Bob work together at their respective rates, approximately how many seconds will it take them to complete the job?
7.17
9.12
11.44
13.77
14
Let the job = 14 units.
Since Adam takes 14 minutes to complete the job, Adam's rate = w/t = 14/14 = 1 unit per minute.
Since Bob takes 14/60 of a minute to complete the job, Bob's rate = w/t = 14/(14/60) = 60 units per minute.
Time for Adam and Bob working together = w/(combined rate) = 14/(1+60) = 14/61 of a minute.
Since 14/60 of a minute = 14 seconds -- and 14/61 is LESS than 14/60 -- the time for Adam and Bob together must be just a bit less than 14 seconds.
The correct answer is
D.
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