9514 1404 393
Answer:
8 days
Explanation:
Assuming the number of days is inversely proportional to the number of people, increasing the number of people by a factor of 25/20 = 5/4 will decrease the number of days by the factor 4/5.
(4/5)(10 days) = 8 days
The provisions will last 8 days if 5 more people join the camp.