"aap" reflect mostly single person. "tum" reflect bunch of person. Kahan kho gaye hain? Kahan means where. kho means disappeared, lost More phrase 1. Kahan chup gaya hai . 2. Koi dikhai nahi de raha hai. check this link: http://www.linguanaut.com/english_hindi.htm Good Luck :) :)

Namaste Leo ji, Aap kaisi ho ? How are U ? In this sentence ' AAP ' (you) is assumed (hidden) since the use of GAYE (form of verb). If U R to make Past tense sentence : TUM KAHAAN KHO GAYAA or THA. However, invariably U use AAP form to give respect. By the way, Do U know the meaning of KHONAA (root verb) ? Pl get back to me. For yr info I am already registered as Hindi Teacher on this site. Can't U see me ? Would U like to have a Hindi session with me. Pl cnfirm Whether U want to take it HERE or on Skype / ym / g-talk etc. My id is ' mdchaskar ' Just add in yr contacts and inform accordingly. dhanaywaad, fir milenge,