Attempted to solve by models 2 questions Monica put forth in the comments section of the previous post. Please let me know if I'm getting any closer to model mode.
1. Maria sold thrice as many $5 files as $10 files. She also sold twice as many $10 files as $20 files. She collected $160 more from selling $5 files than from selling $20 files.
a) How much did she collect from selling $5 files?
b) How many files did she sell altogether?
2. Joyce is 4 years old. Her mother was 25 years older than her last year.
a) In how many years' time will Joyce's age be 2/7 of her mother's age?
b) In how many years' time will Joyce's age be 3/8 of her mother's age?
Note: The difference between the ages of Joyce and her mother is constant at 25 years.