First and foremost, this question is about getting their Least Common Multiple. You can just get it if you want.
Given:
Fried Chicken = prepared every 6 days
Spaghetti = prepared every 4 days
Cake = prepared every 20 days
Asked:
After how many days can the students expect to eat fried chicken, spaghetti, and cake all on the same day?
Solution:
Get the LCM of 6, 4 and 20.
Continuous Division:
| 6, 4, 20
2 | 3, 2, 10
2 | 3, 1, 5
LCM = 2 x 2 x 3 x 1 x 5
= 60
Final Answer:
after 60 days