Answer with explanation:
Time taken by 2, men to build an airstrip = 5 hours
Time taken by 1, men to build the airstrip = 2 × 5
=10 hours
Since ,time is inversely proportional to Number of people working and if rate of doing work is Higher time will be less.
Using Unitary method
![M_{1}T_{1}R_{1}=M_{2}T_{2}R_{2}\\\\R_{1}=R_{2}\\\\T_{2}=4\\\\2 \times 5 \times R_{1}=M_{2}\times 4\times R_{2}\\\\M_{2}=\frac{10}{4}\\\\M_{2}=2.5](https://tex.z-dn.net/?f=M_%7B1%7DT_%7B1%7DR_%7B1%7D%3DM_%7B2%7DT_%7B2%7DR_%7B2%7D%5C%5C%5C%5CR_%7B1%7D%3DR_%7B2%7D%5C%5C%5C%5CT_%7B2%7D%3D4%5C%5C%5C%5C2%20%5Ctimes%205%20%5Ctimes%20R_%7B1%7D%3DM_%7B2%7D%5Ctimes%204%5Ctimes%20R_%7B2%7D%5C%5C%5C%5CM_%7B2%7D%3D%5Cfrac%7B10%7D%7B4%7D%5C%5C%5C%5CM_%7B2%7D%3D2.5)
Number of Men can't be a fraction.So total number of men should be 3 to accomplish the work in 4 Hours.
Earlier 2, men were working to complete the work in 5 days.
Now, 3 men are working to accomplish the work in 4 days.
So,Total number of extra men Added
= 3-2=1
None of the option , matches with the Answer i got.