Not so fast!
If A or B does not do any work, then we have a tie.
Then who is the fastest?
BTW, what is the source of the question.
I know this is the explanation given in the official answer, but I do not agree with that exaplantion. Why do we have to worry about whether A and B actually worked or not. Had the question been "who finished the work fastest"
, I would have agreed with the explanation you are giving. But we just need to decide who is fastest based on the given information. That means whoes speed is maximum. (as one characteristic)
The problme has just two statements of facts. Based on that facts, we just have to tell what is the conclusion. For example, if I tell you that I can do a job in 20 hours and you can do the same job in 10 hours, who is faster? The answer should be you. On the other hand if I ask you who will
finish the job faster or if the work is already done, who finished
the job faster, then I think we do not have any way to answer that. In that case your explanation will hold true.
Please let me know what you think. Thanks