The rate of Glenn in finishing a job would be equivalent to:
Rate (G) = 1 job / 20 minutes
While the rate of Veronika is:
Rate (V) = 1 job / x                ---> x is the unknown
Where 1 job for Glenn means completely cleaning his room while 1 job for Veronika means pulling out everything. Therefore the equation to use would be:
1 / 20 – 1 / x = 1 / 60
The rate of Veronika is subtracted from the rate of Glenn since Veronika is slowing Glenn down. Solving for x:
Multiply both sides by 60 x
(1 / 20 – 1 / x = 1 / 60) * 60 x
3 x – 60 = x
2 x = 60
x = 30
Therefore it takes 30 minutes for Veronika to pull everything out.
I will give you the simple version, if it takes 30 min for the brother to clean and the sister takes 20 minites to mess it up before he cleaned, then the sister messed the room up for 30 min because 30x2= 60.
