"Where were you the day before yesterday?"
Translation:तुम परसों कहाँ थे?
The ending of the sentence depends on the addressing. In Hindi, there are three levels of addressing. Level 1- Addressing someone with utmost respect, we use आप and end with थे or थी depending on gender. 'आप परसों कहाँ थे?' (male) and 'आप परसों कहाँ थी?' (female). Level 2- Addressing a stranger, we use तुम and end with थे or थी depending on gender. 'तुम परसों कहाँ थे?' (male) and 'तुम परसों कहाँ थी?' (female). Level 3- Addressing someone you know, preferably your own age or younger, we use तू and end with था or थी depending on gender. 'तू परसों कहाँ था?' (male) and 'तू परसों कहाँ थी?' (female). We can also use आप for Level 2.
For तुम one uses थी for feminine subject, not थीं? I mean, for showing respect one usually uses plural forms and for masculine it is थे and for feminine थीं.
तुम isn't (necessarily) plural here.
तुम थे - You (masc) were.
तुम थी - You (fem) were.
था and थी are used with the intimate second person pronoun (तू).
Right. That's what I thought as well, but I used था and it was counted as wrong. Perhaps just a glitch in the beta system. I'm not losing sleep over it, haha.