Brain Teasers
E-mails
Mad Ade sends an e-mail to two friends, asking each of them to copy the e-mail and send it to two of their friends, those in turn send it to two of their friends, and so on.
How many e-mails would have been sent by the time 30 sets of e-mails had been forwarded?
How many e-mails would have been sent by the time 30 sets of e-mails had been forwarded?
Answer
2147483646Mad Ade sent the mail to 2 persons. Those 2 sent the mail to 2 persons each, total 4 persons. Now, those 4 person sent mail to a total of 8 persons, then 8 to 16 persons, 16 to 32 persons and so on.... Hence, it a series of 2, 4, 8, 16, 32 up to 30 numbers.
It is a geometric series with a common ratio 2 and first number is also 2. Summation of such series is given by A * (Rn - 1) / (R - 1) where
A = first term
R = common ratio
n = total numbers
So, total number of times mail sent by the time 30 sets of e-mails had been forwarded
= 2 * (2^30 - 1) / (2 - 1)
= 2 * (1073741824 - 1)
= 2 * 1073741823
= 2147483646
Hide Answer Show Answer
What Next?
View a Similar Brain Teaser...
If you become a registered user you can vote on this brain teaser, keep track of which ones you have seen, and even make your own.
Solve a Puzzle
Comments hidden to avoid spoilers.
Follow Braingle!