Marcie started working a part-time job at the beginning of the summer. After four weeks, she increased the number of hours she worked each week by 1/5. After another four weeks, she decreased the number of hours she worked each week by 1/3. From then on, she worked 20 hours weekly. How many hours was she working each week when she began working at the beginning of the summer?

Wait, I got 25 but I see 30 is an option. Let me recheck — after the decrease by 1/3 she works 20, so before that decrease it was 30, right? Then before the increase by 1/5 it was 25. Did I flip the order of the operations?

Took me a second to set this up but working backwards made it click. 20 = (2/3)x, so x = 30 before the decrease, then 30 = (6/5)y for the original.

Is this really 555-605? I feel like the trick is just realizing you reverse the changes rather than applying them forward. Once you see it it's fast.

Can someone explain why we don't just do 20 × 1/3 + 20 to undo the decrease? I keep getting a weird number that way.