Trade is not 'सौदा'
I think 'Trade' means 'धंधा', 'लेन-देन', 'क्रय-विक्रय' and 'व्यापार'('Business' is more appropriate for it) in Hindi. This differs in meaning from 'सौदा'( deal, bargain etc.). But Duolingo is translating Trade as 'सौदा'. I consulted many online sources and books. Not a single source translates 'Trade' as 'सौदा'. There is a small difference in meaning of both the words.
Jattboy, the Shabdkosh dictionary does show "trade" as a translation for "सौदा". (See here). And I checked out a couple of other dictionaries too, and they all show "trade" as a translation for "सौदा". व्यवसाय, कारोबार, लेन-देन and व्यापार are also accepted as alternatives for "trade" though.
This underlines the importance of context. A word may not be an acceptable translation sometimes, but may function well at other times. @Neha_Tyagi's example of "आप किस *सौदे (trade) में है" illustrates where it would be an acceptable replacement. However, the verb "to trade" may sometimes be appropriately translated as "सौदा (noun) करना" : "He traded his cart to buy a horse = घोड़ा खरीदने के लिये उसने गाड़ी का सौदा किया ।" It may also be appropriate in the derived word "सौदागर = tradesman". That may explain the option "trade" in the dictionary entry for "सौदा". ... I understand this 1-year old issue is dead :-)