This is a challenging question that involves rates and ratios. It can be solved easily with algebra but there’s also a model method. Give a try, and let me know if there are any other methods!
Q: A can paint the room in 9h. B takes 6h to paint a similar room. Given both started painting their rooms at the same time, how long will it be before the ratio of the room left to paint for A and B becomes 5 : 3