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A, B and C can do a piece of work in 20, 30 and 60 days respectively. In how many days can A do the work if he is assisted by B and C on every third day?

12 days
15 days
16 days
18 days
Explanation:

As 2 days work =$ \left(\dfrac{1}{20} \times 2\right) $=$ \dfrac{1}{10} $.

$\left(A + B + C\right)$s 1 days work =$ \left(\dfrac{1}{20} +\dfrac{1}{30} +\dfrac{1}{60} \right) $=$ \dfrac{6}{60} $=$ \dfrac{1}{10} $.

Work done in 3 days =$ \left(\dfrac{1}{10} +\dfrac{1}{10} \right) $=$ \dfrac{1}{5} $.

Now,$ \dfrac{1}{5} $work is done in 3 days.

$\therefore$ Whole work will be done in $\left(3 \times 5\right)$ = 15 days.

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