Hi everyone,

I can't seem to get the answers to these questions.

a) Four marbles are in a jar, with the values 0, 1, 10 and 100 printed on them. Push-up Pete will draw a marble each morning and do that many push-ups. What is the probability that he will draw the “100” marble exactly 2 times in a week

b) Four marbles are in a jar, with the values 0, 1, 10 and 100 printed on them. Push-up Pete will draw a marble each morning and do that many push-ups. What is the probability that he won’t have to do push-ups for exactly one week (7 days in a row)

For a) I tried

P(2)=4Cnr2*(1/4)^2*(3/4)^2

=27/128

but this doesn't seem to work.

I'm not exactly sure where to start with b)

Thanks!