Trying to keep this tense (the past imperfect, the था tense) distinct from the simple perfect. The Hindi simple perfect tense seems to translate to the English simple past, and the था tense (past imperfect) seems to translate to "used to" in English. For example, मैं गाता था = I used to sing; मैं गाया = I sang.
But Duo adds a wrinkle here. It seems that Duolingo prefers "was/were" for था when it's the verb होना, and "used to" when it's with any other verb. For example, Duolingo translates तेरी किताब मेज़ पर थी as "The book was on the table," and not "The book used to be on the table." Is this a general rule?
Perfect tense is the past tense conjugation plus हूँ or है . Example: मैं बाज़ार गया = I went to the store (simple past). मैं बाज़ार गया हूँ = I have gone to the store (perfect). मैंने अपना काम ख़त्म किया = I finished my work. मैंने अपना काम ख़त्म किया है = I have finished my work.
Sorry for the late reply, but duo is correct in this sense. You're correct in identifying the past imperfect when a normal hindi verb is combined with था or थी. However when we're talking about state of being, the formation is a bit distinct. तेरी किताब मेज़ पर थी = "Your book was on the table". तेरी किताब मेज़ पर होती थी = "Your book used to be on the table" (a bit of an unused awkward sentence in this case but the rule stands). Hope this helped!
“तेरी किताब मेज़ के ऊपर थी” translates to " Your book was on top of the table " while "तेरी किताब मेज़ पर थी।" translates to " Your book was on the table". Here पर means on and ऊपर means on top. Even in English, people say " on the table " rather than " on top of the table ". Both are correct depending on what you use.