Question

Shira posts a joke on her social network page. Four of her

friends repost the joke on their pages. Four of each of their friends also repost the
joke, and so on. How many people will post the joke on the ninth round?

Answer 1

65536 (people)

Explanation:

Each new count is found by multiplying the previous one by 4. This is a geometric sequence. The general geometric sequence model a(n) = a(1)*r^(n -1) becomes

a(n) = 1*4^(n - 1)

On the 9th round, a(9) people will post the joke:

a(9) = 1*4^(9 - 1) = 65536 (people)

Answer 2

262 144

Explanation:

At each round, there are four times more people reposting the joke. Therefore, we have 4^{9} = 262 144 people reposting the joke on ninth round.