"क्या तुमको पुस्तक मिली ?"
अनुवाद:Did you find the book?
shouldn't it be 'tumhe'? I've heard tumko and tujhko are correct, but I think tumhe and tujhe would be more appropriate. (but in my hindi 'tu' and 'tujhe' and 'tujhko' is not there; I even talk with my school friends using tum. And a stranger even one to two yrs young then me is considered as an 'aap' for me!)
Aadit, you are spot on. In fact, when we corrected the sentence based on AshKanth's feedback, we made the main translation as "क्या तुम्हें पुस्तक मिली?". We do keep तुमको and तुझको as alternate acceptables. Going with Duolingo's playful style, we keep 'तुम' as the main version and 'आप' and even 'तू' as acceptable forms in order to cover the usage styles prevalent throughout the Hindi speaking world.