I was overwhelmed not only by the response, but also by the creativity. While I do not like to single people out, Suman Saraf turned out to be the champion of creativity on this one, had some remarkable variations that I have not seen even on the original source I took the puzzle from (brilliant.org).

The most common answer that Anant Aggarwal, Rahul Rane, Pratik Poddar and Suman Saraf sent me were:

1 + 4! – 9 – 16 (for children, 4! = 1 x 2 x 3 x 4)

Aditya Geevee and Suman Saraf also sent me the following one, which required modification of the right side as well, which most people did not try:

1 – √4 + √9 = √16  (√ stands for square root)

A very good variation of the above sent by Prakhar Prakash:

1 + 4 – √9 = √√16 (means square root of square root of 16)

The cake, as I said, goes to Suman Saraf though for three more variations:

(1 * 4) % 9 = √16 where % is modulo

⎣(√√√(1+4)! * 9)⎦ = 16    i.e. floor(sqrt(sqrt(sqrt((1+4)!))) * 9)

My favourite one from Suman:

1/4% – 9 = 16

I loved the answers, hope you all enjoyed this puzzle!