Question 941108
It takes 49 minutes for 4 people to paint 7 walls
--------------
It takes 49/9 min for 36 people to paint 7 walls
--------------
It takes ( 4/9)*49 min for 9 people to paint 7 walls
--------------
It takes (1/7)*(4/9)*49 min for 9 people to paint 1 wall
--------------
It takes (9/7)*(4/9)*49 min for 9 people to paint 9 walls
--------------
{{{ (9/7)*(4/9)*49 = 28 }}}
It takes 28 minutes for 9 people to paint 9 walls
===============================
Actually this is the same time for 1 person to paint 1 wall
--------------
It takes 4*49 min for 1 person to paint 7 walls
--------------
It takes (4/7)*49 min for 1 person to paint 1 wall
{{{ (4/7)*49 = 28 }}}
It takes 28 min for 1 person to paint 1 wall
Good thing to remember