Question

On Saturday, you download a video and e-mail it to seven friends. On Sunday, each of these friends emails the video to seven more friends. Each person who receives the video on Sunday emails the video to seven people on Monday, and so on. After 7 days, how many people have received the video?

Answer 1

137,257 people have received the video.

Explanation:

Since, the number of videos receive on saturday = 1,

On Saturday, the video are mailed to 7 persons,

So, the number of videos receive on saturday = 7,

On Sunday, each person mail the video to further 7 persons,

So, the number of videos receive on saturday = 49,

Now, on monday each person mail the video to further 7 persons,

So, the number of videos receive on monday = 49 × 7 = 343,

Thus, there is a series that represents the given scenario,

1, 7, 49, 343,....

Which is a GP, having first term, a = 1,

Common ratio, r = 7,

For finding the total number of received videos after 7 days,

Number of terms, n = 7,

Hence, the number of received videos after 7 days,

`S_(7)=(a(r^n-1))/(r-1)`

`=(1(7^7-1))/(7-1)`

`=137257`

Therefore, 137257 people have received the video.