12 Days of Christmas GMAT Competition - Day 7: 40 skilled employees ne

Given:
40 skilled employees need 60 days to complete a project while working in the normal work schedule of 8 hours a day.
They begin working but one month into the project, 30 employees need to shift to a different project.
These 30 employees are replaced by 40 new employees who are 50% less productive.

Asked: How much extra time per day should the new team work to avoid any delay in the completion of the project?

40 skilled employees need 60 days to complete a project while working in the normal work schedule of 8 hours a day.
Work done by 40 skilled employees in 1 month while working in the normal work schedule of 8 hours a day = 1/2

They begin working but one month into the project, 30 employees need to shift to a different project.
These 30 employees are replaced by 40 new employees who are 50% less productive.
40 new employees who are 50% less productive = 20 effective employees with full productivity
40 - 30 = 10 employees remained
Number of effective employees with normal productivity remaining = 10 + 20 = 30 employees

20 + 10 = 30 employees will require time for completion per day = 40/30*8 = 32/3 = 10 2/3 hours = 10 hours 40 minutes
The extra time per day should the new team work to avoid any delay in the completion of the project = 10 hours 40 minutes - 8 hours = 2 hours 40 minutes.

IMO D

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