Question 1128472

{{{ A= P( 1 + r )^t}}} 

{{{t=2}}} years 

{{{P=2000}}} grows to 

{{{A=3380}}}

{{{r}}}=?


{{{ 3380= 2000( 1 + r )^2}}} 

{{{ 3380/2000=( 1 + r )^2}}} 

{{{ 1.69=1 + 2r +r^2}}} 

{{{ r^2+ 2r +1-1.69=0}}} 


{{{ r^2+ 2r-0.69=0}}} 

{{{ 100r^2+ 200r-69=0}}} 


{{{r = (-200 +- sqrt( 200^2-4*100*(-69) ))/(2*100) }}} 

{{{r = (-200 +- sqrt( 40000+27600 ))/200 }}} 


{{{r = (-200 +- sqrt( 67600 ))/200 }}} 


{{{r = (-200 +- 260)/200 }}} 

{{{r = (-10 +- 13)/10 }}} ...need only positive solution


{{{r = (-10 + 13)/10 }}} 


{{{r = 3/10}}}


{{{r=0.3}}} => {{{r=30}}}%