Question 560089
If 5 cooks take 6 hours, then 
1 cook will take 5 times longer, so
1 cook takes 30 hrs to prepare the food
9 cooks will take 1/9 of that time , so
9 cooks will take {{{ 30/9 = 10/3 }}} hrs
9 cooks will take 3 1/3 hrs or 3 hrs and 20 min
This is an example of inverse variation because
( number of cooks ) = {{{k}}}*( 1/ ( time to prepare dinner )
where {{{k}}} is some constant