Question 1167305
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Josef’s father is seven times as old as he is. One year ago, he was nine times as old as Josef.  Find Josef’s present age?
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f is k times as old as x.   p years ago, f-p was v times as old as  x-p.
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{{{system(f=kx,f-p=v(x-p))}}}
{{{Find}}}{{{x}}}.


{{{kx-p=v(x-p)}}}
{{{kx-p=vx-vp}}}
{{{kx-vx=p-vp}}}
{{{x(k-v)=p-vp}}}

{{{highlight_green(x=(p-vp)/(k-v))}}}



{{{system(k=7,p=1,v=9)}}}
{{{substitute}}}.


{{{x=(1-9*1)/(7-9)}}}

{{{x=(-8)/(-2)}}}

{{{highlight(x=4)}}}