On the first day of a water polo tournament, ticket sales totalled $17,610. One-day passes sold for $20 and tournament passes for $30, and the number of tournament passes sold was 37 more than the number of day passes. How many one-day passes were sold?

1. Let d stand for the number of day passes, so the number of tournament passes is d plus 37. 2. Each pass type contributes its price times its count, so the money equation is 20d plus 30(d plus 37) equals 17,610. 3. Distribute the 30: 20d plus 30d plus 1,110 equals 17,610. 4. Combine like terms: 50d plus 1,110 equals 17,610. 5. Subtract 1,110 from both sides: 50d equals 16,500. 6. Divide by 50: d equals 330, so 330 one-day passes were sold. 7. Check: 330 day passes bring in $6,600 and 367 tournament passes bring in $11,010, and 6,600 plus 11,010 equals $17,610. 8. 367 is the number of tournament passes, not day passes, which is the classic trap of reporting the wrong unknown. 9. 352 comes from dividing 17,610 by 50 while ignoring the 37 extra tournament passes entirely. _Source: OpenStax Prealgebra (CC BY 4.0), Ch 9 "Math Models and Geometry", section 9.2 Solve Money Applications_