My project manager assigned me a task to estimate the development time for an iPad application. Lets assume that I gave estimation of 15 working days. He thought that the number of days where too many and client needed the changes to the application urgently (as in most of cases).

So, he told me: "I am going to assign two developer including you and as per my understandings and experience it won't take more than seven working days."

Clarifications

I was given the task of estimating development time for an individual. How could I be sure that 2 developers are going to finish it within 7 days? (I am new to team & I hardly know the others abilities)

Questions

• Why do most of project managers / team leaders have understandings like:
  • If one developer requires N days,
  • Then two developers would require N/2 days,
• Do they think something like developer = s/w production machines?
• Should a team member (developer, not team lead or any higher post) estimate other developers work?

I didn't deny anything in the meeting and didn't said, but what should be the appropriate answer to convince them that N/2 formula that they follow is not correct?