there're usually exams for multiple subjects at the same time, with each subject occupying one or more 49-seat blocks. There're some 25 or 30 blocks in total...
about the sheet, my guess is the table was a bit wobbly so they put some paper under the leg
I had to laugh when I read drd's comment about "educational nightmares"... It is a bit overwhelming in its institutional feel! However, your photograph - the image is a great one - love all those wooden chairs - the lines of the tiled floor and the ceiling's light panels! Nice white balance - for me, the warmth makes it much less scary...than my nightmares of missing The Exam and/or The Matrix.