bb wrote:

Explanation:

Official Answer: C

After 2 minutes 2*\frac{1}{10}=\frac{1}{5} of the taks will be done (as only A works);

After 4 minutes \frac{1}{5}+2*(\frac{1}{10}+\frac{1}{5})=\frac{4}{5} of the task will be done and \frac{1}{5} will be left to be done;

We are told that 1/5th of the task is done in 15 minutes (1/4th of an hour) by all three workers: \frac{1}{4}*(\frac{1}{10}+\frac{1}{5}+\frac{1}{x})=\frac{1}{5}. From which we can find that x=2 hours.

Answer: C.

sorry fellow, this is my very first time comment here

could you please explain why do you use minutes if in statement said hours. I mean after 2 and after 4 hours.

thanks for helping out

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