Question

100 workers can make a bridge in 150 days. When 20% bridge was completed 25% workers left the job, find the number of days in which remaining work will be completed by remaining workers. (All workers have the same efficiency)
1. 100 days 
2. 130 days 
3. 160 days 
4. 250 days 

Answer 1

Correct Answer - Option 3 : 160 days 

Given : 

100 workers can make a bridge in 150 days.

Concept used : 

Total work = Working efficiency × Total working time 

Calculations :

Let the work efficiency of each worker be 'x' unit per day 

Total work done by 100 workers per day = 100 × x = 100x units 

Total work = 100x × 150 = 15000x units 

25% workers left the job after 20% bridge completion 

Remaining work = 100% - 20%

⇒ 80% of 15000x = 12000x units 

Remaining workers = 75% of 100 = 75 

Time taken by 75 workers to complete the remaining work = 12000x/75x = 160 days

∴ Option 3 will be the correct answer.