How is 3 hours and 15 minutes equal to 3.25?

Answer 1

Hours and minutes are in base 60. On the other hand 3.25 is in base 10. Doing the conversion bringing everything to minutes we have 3 hours * 60 + 15 = 195 minutes. Finally, 195/60 = 3.25. In fact the conversion is not necessary: since 15 minutes is a quarter of an hour, 0.25 also represents a quarter of a unit in base 10. A conversion to base 10 might be useful for adding and subtracting time on a computer but that's pretty much where the usefulness ends as 3.25 hours (i.e. 3:15) is different than 3:25. For example 4:10 - 2:55 = 1:15 might be reduced to 4.1667 - 2.9167 = 1.25 which converted back in time unit is an hour an a quarter or 1:15. Doing the opriginal calculation on a computer would give you 4.10 - 2.55 = 1.55 or 1:33 which would be wrong by 18 minutes.