Question 1206057
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        Be careful :   this problem is a trap.


        The trap is that this sequence is  SPECIAL :   it  IS  an arithmetic sequence, 
        but starts from the zeroth term  20.


        Therefore,  the formula for the n-th term must be modified.



<pre>
The standard formula {{{P[n]}}} = 20 + (n-1)*35  does  {{{highlight(highlight(NOT))}}}  work now - it should be modified.


    +---------------------------------------------+
    |   The correct formula is P[n] = 20 + n*35   |
    +---------------------------------------------+


Again, your correct explicit formula is  {{{P[n]}}} = 20 + n*35.


You can  {{{CHECK}}}  it:  {{{P[1]}}} = 20 + 1*35 = 20 + 35 = 55.


In particular,  {{{P[100]}}} = 20 + 100*35 = 3520.
</pre>

Solved.


The solution and the calculations by @MathLover1 are &nbsp;INCORRECT &nbsp;and lead you to &nbsp;WRONG &nbsp;answer.


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For introductory lessons on arithmetic progressions see 

&nbsp;&nbsp;&nbsp;&nbsp;- <A HREF=http://www.algebra.com/algebra/homework/Sequences-and-series/Arithmetic-progressions.lesson>Arithmetic progressions</A>

&nbsp;&nbsp;&nbsp;&nbsp;- <A HREF=http://www.algebra.com/algebra/homework/Sequences-and-series/The-proofs-of-the-formulas-for-arithmetic-progressions.lesson>The proofs of the formulas for arithmetic progressions</A> 

&nbsp;&nbsp;&nbsp;&nbsp;- <A HREF=http://www.algebra.com/algebra/homework/Sequences-and-series/Problems-on-arithmetic-progressions.lesson>Problems on arithmetic progressions</A>  

&nbsp;&nbsp;&nbsp;&nbsp;- <A HREF=http://www.algebra.com/algebra/homework/Sequences-and-series/Word-problems-on-arithmetic-progressions.lesson>Word problems on arithmetic progressions</A>

in this site.