Question

It takes six analysts forty-two days to write a report. If the report had to be ready in 7 days, how many analysts would be needed?

Answer 1

If you assume doubling the workers will halve the time taken to finish then 12 analysts will take 21 days
To finish in 7 days (1/6 of 42 days) you would need 6 x the original number = 36 analysts.

Brook’s Law (see Wikipedia) suggests than adding extra analysts will actually slow the project down!
One reason is the extra people tend to get in each others way.