Rule of tree 350 chefs have worked 6 hours a day, preparing 1,500 dishes in 10 days. 420 chefs working 8 hours a day, how many dishes can you prepare in 18 days?

Hi!

Let's find how many dishes the chefs can prepare in 1 hour.

10 x 6 = 60
They work 60 hours in 10 days. 
1,500/60 = 25
They cook 25 dishes in one hour. 

If 420 chefs are working 8 hours a day, for 18 days they can prepare how many dishes? 

18 x 8 = 144
144 hours in 18 days. 
144 x 25 = 3600

You can prepare 3600 dishes in 18 days. 

Hope this helps! :)