Answer: 5 (first round) + 25 (second round) + 125 (third round) + 625 (fourth round) = 780
So, at the end of 4 rounds, including Jacob himself, 780 people will have gotten fliers.
Step-by-step explanation: In the first round, Jacob hands out fliers to 5 people.
In the second round, each of the 5 people from the first round hands out 5 fliers to 5 other people. So, there are now 5 x 5 = 25 people with fliers (including the original 5).
In the third round, each of the 25 people from the second round hands out 5 fliers to 5 other people. So, there are now 25 x 5 = 125 people with fliers (including the original 5 and the 25 from the second round).
In the fourth round, each of the 125 people from the third round hands out 5 fliers to 5 other people. So, there are now 125 x 5 = 625 people with fliers (including the original 5, the 25 from the second round, and the 125 from the third round).