Respuesta :

It's basically a proportion/rate/ration problem so here:

3 people : 15 days = 5 people : x days

So first find how many days it takes with 1 person and you can do so by division:
1 person : 5 days

Now multiply by 5 people:
1 person : 5 days = 5 people : 25 days

Hope that helps