Question 1134943
Formula for sum:
{{{ s = a* ( 1-r^n)  / ( 1 - r ) }}}
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{{{ 100a = a*( 1-r^n)  / ( 1 - r ) }}}
{{{ a*r^n = 9a }}}
{{{ r^n = 9 }}}
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{{{ 100 = ( ( 1-r^n) ) / ( 1 - r ) }}}
{{{ 100 =  ( 1 - 9 ) / ( 1 - r ) }}}
{{{ 1 - r = -8 / 100 }}}
{{{ -r = -.08 - 1 }}}
{{{ r = 1.08 }}}
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{{{ 1.08^n = 9 }}}
{{{ n*log( 1.08 ) = log(9) }}}
{{{ n = log(9)/log( 1.08 ) }}}
{{{ n = log(9)/log(1.08) }}}
{{{ n = .9542425 / .0334238 }}}
{{{ n = 28.55 }}}
29 terms
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check:
{{{ 100 = ( ( 1-r^n) ) / ( 1 - r ) }}}
{{{ 100 = ( ( 1-1.08^29) ) / ( 1 - 1.08 ) }}}
{{{ 100 =  ( 1 - 9.31727 ) / (-.08) }}}
{{{ 100 = 8.31727 / .08 }}}
{{{ 100 = 103.96 }}}
I used {{{ 29 }}} instead of {{{ 28.55 }}}
That's the error, I think. Definitely get
a 2nd opinion on this.