Work done by A in one day is half of the work done by B in one day Work done by B is half of the work done by C in one day If C alone can complete the work in 7 days in how many days can A B and C together complete the work ?
Let the speed of work done by A, B and C be a, b and c.
Now, b=.5c, a=.5b=.25c
c does work in 7 days. It's speed will be W/7. A's speed will be .25W/7 and B's speed will be .5W/7
Their combined speed is 1.75W/7
Time taken by them to complete the work = $$\frac{W}{(1.75W/7)}$$ = $$\frac{7}{1.75}$$= 4
Hence, together they will complete the work in 4 days.
Therefore, option C is correct.
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