Test for Prerequisites

Here are two problems which can be used to judge whether you have 
the required prerequisites. If you do not have clues about the 
solutions to these two problems, you do not have the right 
prerequisites. 

(1). In a noisy classroom, the instructor talks to a student, say 
A, with a success rate 90% for each sentence, how many times on 
average does the instructor have to repeat the same sentence? 

(2). Given S(t)=0.5sin(2*pi*900.15t+2*pi/3),  what is the amplitude? 
the frequency? the phase? If your cellular phone is allocated a 
channel at [900.10,900.20] MHz range, can you receive this signal?