Question 1193425
<pre>
{{{ F = P(1+r*t) }}}

10000 = 1250(1+0.125t)
7 = 0.125t
t = 7/0.125 = {{{ highlight( 56 ) }}} yrs

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Side note:

A good opportunity to show why compounding interest is so powerful.  If the interest is compounded (even if just once per year), you get this:

   {{{  F = P(1+r/n)^(nt) }}}
   {{{ 10000 = 1250(1+0.125/1)^(1*t) }}}
   {{{    8 = 1.125^t }}}
   {{{ ln(8) = t*ln(1.125) }}}
   {{{   t = ln(8)/ln(1.125) }}}
   {{{   t = 17.65 }}} years   (less than one third the time of simple interest)