[pd] [noise~],[expr~], questions

sorry, i have a few questions today, i know it's bad from to ask them all in one thread, but i don't want to start too many threads.

question 1) how do you multiply a signal by a power of n ? can you do it with expr~?

question 2) is there a list of the functions that i can use with expr~ (and expr) ? i have seen many of these functions in other peoples patches, but can't find them in pd's documentation.

question 3) i want to insert a percentage of random noise into a signal. ie, for every oscillation of an [osc~] i want 25% of the samples to be converted into noise. the level and position of the noise should be random, but 25% of the samples in each oscillation must be be converted into noise. any idea how to do that?

thanks for any help.