Question

Arun can finish a work in 36 hours and Ballu is twice as efficient as Arun. If they work together, how many hours they will take to finish the same work?
1. 10
2. 12
3. 15
4. 18

Answer 1

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