SOLUTION: Linda starts a chain letter and sends it to three friends. Each of the three friends sends the letter to 3 other friends and the sequence is repeated. Assuming that no one breaks

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Question 1165079: Linda starts a chain letter and sends it to three friends. Each of the three friends sends the letter to 3 other friends and the sequence is repeated. Assuming that no one breaks the chain, how many letters will have been sent from the first through the sixth mailings?
Answer by ikleyn(52832) About Me  (Show Source):
You can put this solution on YOUR website!
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The sum of the 7 first terms of the geometric progression with the first term 1 and the common ratio of 3.

Use the formula for the sum.

On geometric progressions,  see introductory lessons
    - Geometric progressions
    - The proofs of the formulas for geometric progressions
    - Problems on geometric progressions
    - Word problems on geometric progressions
in this site.

Also,  you have this free of charge online textbook in ALGEBRA-II in this site
    - ALGEBRA-II - YOUR ONLINE TEXTBOOK.

The referred lessons are the part of this online textbook under the topic
"Geometric progressions".

Save the link to this textbook together with its description

Free of charge online textbook in ALGEBRA-II
https://www.algebra.com/algebra/homework/complex/ALGEBRA-II-YOUR-ONLINE-TEXTBOOK.lesson

into your archive and use when it is needed.