Treasure Hunt

They patiently waited for the event to start. It had been 30 minutes, but there still wasn't any sign of the mysterious voice. By this time, there were already almost 50 students in the room. The atmosphere was getting tense. He recognized some of them while others were a complete mystery to him.

 "Time is up. Under the desks, you will find instructions. You only have 30 minutes," and the voice was gone again as fast as it came. Linri pulled out a paper from under the desk he was sitting at. On it, there were 20 riddles and some instructions. Solve the riddle to bla bla bla. You have to shout the answer bla bla bla. Anyway, he was finally ready to go.