.
The proportion
=
express the rate of work for each of the two scenarios.
It is equivalent to
= ,
= ,
x = 45.
Answer. 45 minutes.
This method is a) simplest and b) it works ALWAYS.
So, I recommend it to you for using in the most difficult cases.
To see more solved problems of this type, look into the lesson
- Rate of work problems
in this site.