Suppose someone opens an email infected with a virus Each ti

Suppose someone opens an email infected with a virus. Each time the email is opened it is sent out to 9 other people. Some people open the infected email, but others do not How many people have opened the infected email, including the first person, if no one receives more than 1 email and if the email ends after there have been 89 people who receive the email, but do not open it? You must show your reasoning/formula used.

Solution

Ans : 11

When the first person opens the mail 9 persons receives the mail.

Now among the 9, 1 person opens = 9 new persons + 8 previous persons haven\'t opened = 17 persons

among 17, 1 person opens, = 9 new + 16 old = 25 person have not opened

now among 25, 1 person opens, = 9 new + 24 old persons have not opened

continuing this way...

we have 80 old persons and 9 new persons who will be having the mail but didn\'t open; with only 11 old persons who opened the mail.