Four workers can build a stage in 10 eight-hour days. At the same rate, how many workers will it take to build the stage in 5 eight-hour days?
To get it done in HALF the time will take TWICE as many workers. 8 workers.
ElectricPavlov is correct.
One way to analyze the problem:
Each worker worked 10 eight-hour days for a total of 80 hours (10 x 8).
Since there were four workers, they worked a total of 320 hours.
If you want to build the stage in 5 eight-hour days, each worker needs to work 40 hours (5 x 8).
The total number of hours needed is still 320 hours; since each worker works 40 hours, calculate 320 / 40 to get 8.
You will need 8 workers.