10000 = 1250(1+0.125t)

7 = 0.125t

t = 7/0.125 =  yrs



========================



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:



   

   

   

   

   

    years   (less than one third the time of simple interest) 

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