Correct Answer - Option 2 : 12
Given-
Time taken by Arun to complete the work = 36 hours
Ballu is twice as efficient as Arun
Formula Used-
Total Work = Efficiency × Total Time
Calculation-
Part of work done by Arun in 1 hour = 1/36 [If total work is assumed to be 1]
Part of work done by Ballu in 1 hour = 2 × 1/36 ∵ Ballu is twice as efficient as Arun
⇒ 1/18
Part of work done by Arun and Ballu in 1 hour = 1/36 + 1/18
⇒ 3/36
⇒ 1/12
∴ Time taken by both of them to complete the whole work = 1/(1/12)
⇒ 12 hours