04 Try it yourself Interactive

The same job, staffed differently

This console works the basic together-time case, and the reason it belongs here is the invariant: change who is working and the job’s size in units never moves. Add a third worker and watch the total units stay fixed while the time falls — that is inverse proportion made visible.

Two people who each take 8 days
8 units · 4 days — exactly half
The total-units figure is the job. It does not change when you add or remove workers, which is exactly why persons and days multiply to a constant.
Press Next to work through it one step at a time.
Total units–
Units/day–
Together–
Answer–
step 0 / 0