IKMC 2027 - Grades 7-8 - Self-study SET 5 - Thematic Batch 3 Question 9

Boo’s turtle family initially has 12 members and prepares food for a 20-day hike up Fansipan. Some of Boo’s friends join the trip, and the food now lasts only 15 days. How many friends join, assuming everyone eats the same amount per day?