The Award for the Best Duet of 1940 goes to?
If you look at the broad statistics in my Overview Post on the best songs of 1940, you would see out of total 351 songs in the year, whose singers are identified, the ratio of male solos, female solos and duets are 1:1.47:1.19. This may not follow the long-term average of male solos to female solos to duets, but it does follow the general trend that female solos far outnumber male solos, and duets too are generally much more than male solos. Whether 19% differential of the duets over male solos is statistically significant or not is best left to the professional statistician. But I have mentioned several times that in music the impact of a particular singer is not necessarily commensurate with statistics. This phenomenon was particularly pronounced in the era of KL Saigal and Pankaj Mullick when their songs pulled their weight much above their numbers.READ THE FULL ARTICLE
The year 1940 also shows preponderance of Female Solos over Male Solos in total numbers, in line with the long-term trend, as evident in the list of MEMORABLE SONGS in the 
1940 was a year of churning in the film world. It came at the transition of the first decade of spoken films, 1930s, and the beginning of the 1940s. It was a churning of musical styles when one kind of music making was coming to an end, and another was showing its sprouts. There was also a churning in established studios like the Bombay Talkies – because of the death of its owner Himanshu Rai; and the New Theatres of Kolkata, which was struck by a fire destroying most of their prints. However, these tragedies did not deter them from creating some great films and outstanding music. I have written about the general scenario in my 
This is the transition year between the 1930s and 1940s. This was the year when Himanshu Rai, the founder of Bombay Talkies, passed away. The internecine war in the studio had not yet begun. So Bombay Talkies was going great guns with Ashok Kumar and Leela Chitnis with films like Aazad, Bandhan with music by Saraswati Devi and Ramchandra Pal. Ramchandra Pal working solo also gave outstanding music for Punarmilan with a great twin song Naacho nacho pyare man ke mor (by Arun Kumar/Snehprabha Pradhan). I don’t know whether it was the first twin song of Hindi films, but I can say without hesitation and disproving my general hypothesis, that both the versions are equally good.