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C alone can complete a work in 20 days and D alone can complete the same work in 30 days. In how many days C and D together can complete the same work?

A6 days

B12 days

C15 days

D8 days

Answer:

B. 12 days

Read Explanation:

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Calculation:

LCM of 20, 30 = 60

Let the total work be 60 units

⇒ Efficiency of C = 60 / 20 = 3 units / day

Efficiency of D = 60 / 30 = 2 units / day

Efficiency of C and D when working together = 3 + 2 = 5 units / day

∴ Time taken by C and D when working together = 60 / 5 = 12 days.


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