find the number of days 4 workers can complete a job if 10 workers can complete the job at in 2 days

Answer 1

4x = 10*2
x = 5 days
or,
2/5 the workers, so 5/2 the time: 5/2 * 2 = 5

Answer 2

8 days for 4 workers to complete a job
4x2=8