Question 818271
You can write a proportion:
{{{ (1/5) / 10 = 20 / d }}}
This is ( sec / ft ) = ( sec / ft ) 
Multiply both sides by {{{ 10d }}}
{{{ (1/5)*d = 200 }}}
{{{ d = 1000 }}}
The dog can run 1000 ft in 20 sec