Question

Will two separate 50dB sounds together constitute a 100dB sound?

Answer 1

No, because the dB scale is logarithmic, not linear.

Answer 2

No, two separate 50dB sounds together do not constitute a 100dB sound because dB is an exponential scale as said by @vincent-lyon.Fr . Each ten dB increase in sound makes the sound ten times louder. An increase of 50dB makes the sound 104 times louder. Hence it will not make 100dB but twice as loud is an increase of 10Log (2) = 3.01dB. So 53.01dB is twice as loud as 50dB.