Name: DiLlOn

Who is asking: Student
Level: Middle

In the city of Skangai there are 6 million people.Each person has to tell 2 more people that theres going to be an earthquake. After they do they leave the city. There will be no duplications.It takes 3 minutes to tell each person. How long will it take for the whole city to know about the earthquake?


Hi Dillon,

I would use a table to keep track of the first few steps.

Time in
Number toldPopulation remaining
016 000 000
325 999 999
645 999 997
985 999 993
12165 999 985

This seems very slow but it soon picks up. I have done 5 rows of the table and you don't need to go far beyond the 20th row.

Can you see a pattern that allows you to solve this problem without constructing the table?

Go to Math Central