1. The problem statement, all variables and given/known data We're driving with a Uav of 80 km/h The duration Δt is 2 h 45 min On a rainy day, our Uav' is 65 km/h If the distance is the same, how much more is the duration of the drive? So, technically we want the result of Dt = Δt' - Δt 2. Relevant equations Uav = Δx / Δt 3. The attempt at a solution 1 h -> 60 min => 2 h -> 120 min => Δt = 165 min Uav = 80 km/h = 80/60 km/min Uav' = 65 km/h = 65/60 km/min Uav'*Δt' = Uav*Δt <=> 65/60 km/min * Δt' = 80/60 km/min * 165 min <=> Δt' = (80 * 165) / 65 min= 203 min Dt = Δt' - Δt = (203 - 165) min = 38 min I also tried turning km to meters, I tried turning 2 h 45 min to 2,75 h, everything. But I still get the same result, every time. Okay, so, as it's evident it's a simple exercise. The problem is, I've run it 5 times or so, but I get a different result from the book's (no complete solution there, just the end result). The book says that we spent 43 min extra on the road. Personally speaking, on most occasions (sometimes I approach it with h, and others with min) I get 38 min extra. So, yeah, am I missing something, or does the book have a typo? PS: It's exercise 2.3 of Hugh D. Young's University Physics, Vol 1 PS2: If anyone has this book, is there any reason why it has the answers only for the odd number exercises? PS3: If it's of any importance, the book has been translated into Greek from English. You can see from my use of the formulas/equations that I'm still a little wonky on how to accurately write them in their correct form, but University has started for about a month, and the teachers move so fast (in one month, out of the 12 sections, the Physics teacher has already passed the 8th one, so, yeah...) that I'm stuck on my own. Every bit of help would be greatly appreciated!