A project is expected to be completed by 9 people in 16 days, but three workers will be reduced after two days. Q: How many days will it take to complete?

If a person's daily workload is 1, then the total workload is 9 *16 *1=144.

Two days later, there will be:144-2 * 9 *1=126.

Then the remaining days are:126/[(9-3) *1] = 21day.