Correct both of you. Thanks.
I probably missed something here...here is my logic
=>In one day the 4 guys do 10% of the job (half div by 5 days )
=>each of the 4 men does 2,5% of the job per day
=>if they are 10 that makes 25% of the job per day
=>so I come to 4 days needed
can someone help track the issue in my approach?
You almost got it. What you missed is the fact that half the job is already done, and that the question asks you to find how much time it will take 10 men to do the remaining half of the job.
Your answer of 4 days is for the complete job.
Therefore 10 men will take 2 days to complete half of the job.