Lizzy: Grace can read a 200-page book in 20 hours. How long would it take her to finish reading a 250-page book at this constant rate?.
Me: Hmmm, let me think. I think this is the detailed solution:
Grace can read 200 / 20 = 10 pages in 1 hour. So she can finish a 250 - page book in 250 / 10 = 25 hours. Final answer: 25.