"Auto mého táty je rychlejší."

[Sammka]

Why not 'my father's car is faster'?

[kacenka9]

I believe that it is because FATHER is more formal and equals OTEC in Czech.

Auto mého otce je rychlejší.

[JamesTWils]

And yet, sadly, I do not recall being introduced to either otec or the word for mother. I would suggest that the standard word for the relationship should always be accepted. I suppose, though, that you could include dad, pa, da, poppa, daddy, and every other less formal term for the word father.

[Sammka]

Makes sense - It's just a bit confusing because in other parts of Duolingo they seem to treat those words interchangeably.