I saw this very interesting vort the other day:
A reason for this custom:
????=199
The minimum requirements for a Kosher Sukkah is as follows:
Two complete walls of 7 by 10 (7×10 ?????)
[The width needs be 7 and the height 10]
7 x 10 = 70 times two = 140
The third wall could be even just one ???
1 X 10 = 10
The Sechach needs to be 7 x 7 =49
140+10+49= 199
The same Numerical value as ????