conuly

Depends. Maybe the same publisher is also publishing a 4th-grade Science textbook which explains thermometers and the history of different systems quite early on, so by the time a class reaches these math problems, they'd definitely know all that. The people who wrote the textbook probably expected that a responsible teacher would ask the kids whether they knew about thermometers, and if they didn't, would explain the basics...

... yeah, maybe that was a bit much to assume. *ducks*