Correct Answer - Option 3 : 12
Given :
Ram can do the work in 20 days
Shyam can do the work in 25 days
Concept used :
Total days took to complete the work = Total work/work done each day
Calculations :
Total work = LCM of 20 and 25 = 100 units
Ram’s per day work = 100/20 = 5 units
Shyam’s per day work = 100/25 = 4 units
Ram’s and Shyam’s each day work = 5 + 4 = 9 units
Total work done by them in 8 days = 8 × 9 = 72 units
Now Shyam got an injury
Remaining work = 100 – 72 = 28 units
Shyam’s efficiency after 8 days = 50% of 4 = 2 units
Now Ram’s and Shyam’s each day work = 5 + 2 = 7 unit
Days required to complete the remaining work = 28/7
⇒ 4 days
Total days = 8 + 4 = 12 days
∴ Total number of days taken by them is 12
