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:
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.