Question 1193987
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As I read this problem formulation,  I see  FATAL  DEFICIENCIES  in its formulation.


From the problem's description, it is unclear, if it is an Ordinary Annuity, which accumulates 
deposits making regular compounding semi-annually, or it is a Sinking Fund, which provides 
outpayments semiannually. From the text, it is impossible to determine/(to distinct), 
which version is considered.


Second note regarding the formulation: it asks "find the sum of these values".
- Find the sum of  WHICH  values ?    In problems of this kind, a question is  NEVER  posed this way.
If an  Ordinary  Annuity is considered,  then normally the problem should ask to find the future value.


So, my conclusion regarding the problem formulation is that its formulation is   FATALLY  ILLITERATE.


It is not appropriate form for a  Math problem,  and is not appropriate form to post to the forum.


Now,  about the solution.


The  "tutor"  @parmen considers it as an  Ordinary  Annuity, but for some reason,  unknown to me, 
calculates the  Present  Value instead of the  Future  Value,  which makes few sense  (if any).  
In this situation,  the solution normally should calculate a  Future  Value.



Besides of this,  in the solution by  @parmen,  there is a systematic error in all calculations.



From the end of the 3-rd year to the end of the 9-th year, there are 

    2*(9-3)+1 = 2*6+1 = 13 semi-annual payments - not 12.



From the end of the 3-rd year to the end of the 5-th year, there are 

    2*(5-3)+1 = 2*2+1 = 5 semi-annual payments - not 4.


Regarding the solution, I think that is not appropriate for a human-tutor or for an AI-tutor 
to treat such problem without adequate explicit comments/corrections of its formulation,
as well as it is not appropriate to make such errors.


Again,  my conclusion after writing these my notes is that the problem formulation is illiterate

and the solution treats the problem incorrectly from pedagogical point of vies and is also  INCORRECT  in its essence.



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I have a mathematical education (MS in Math) from renowned university, 
PhD degree in Physics and Mathematics, and I worked internationally 
and in the US for many years as a computer engineer in Civil Engineering.


Our major everyday task/duty was performing/supporting numerical simulation for complex phenomena
in Civil Engineering (from conductive heat transfer, phase changes, natural and forced convection, radiation heat exchange 
to stability of engineering constructions, including hydrodynamics, liquid sloshing, elastic stress and strain in solids, 
vibrations, fluid-structure interactions etc.)


Our other everyday task/duty was to make mutual cross-checking to calculations of other colleagues.


I can say, based on my experience, that with such errors, that AI makes every day at this forum, such a colleague 
would be fired in the next day - - - because other colleagues and consumers would ask the management to do it.



I say these words not to offend you personally.


In opposite, working on your posts and checking your solutions, I am on your side and work for your benefits.


I simply want to correctly and adequately describe you the current state/level/status of your artificial intelligence.