Challenge problem · non-routine

Answer: 4.55 %

1. Last year: $400 \times 55 = 22{,}000$; this year: $400 \times 57.50 = 23{,}000$.
2. Increase: $1{,}000$; percentage $= 1{,}000/22{,}000 \approx 4.55\%$.
3. The percentage equals the change in the rate itself: $2.50/55 \approx 4.55\%$.