I assure you, Project is very good at math.

As I have tried to explain, you have a mismatch between your Project calendar (Project Ribbon, Change Working time) and your definition of a day and week. Zooming in to the Gantt chart is not a substitute for looking at both your options settings (File > Options, Schedule) and your calendar.

So - what is your working time in your calendar. (Please check - Project Ribbon, Change Working time.)

What is your definition of day and week - File > Options, Schedule.
What is your default start time?
What is your default end time?