(a) 3Mbps / 150Kbpa

=3 X 1024 / 150

=3072 / 150

=20.48

20 Users can be supported 150Kbps dedicated.

(b)

(i) Each user transmits only 10% of the time, means a user is idle in 90% of the time, transmits in 10% of the time.

\therefore The Probability P=10%

(ii) Using Binomial Distribution,

P(X=n)=\binom{120}{n}p^{n}\left (1-P)^{120-n}

Where P is the Probability of one user is transmitting.

(iii)

We need to calculate P(X\geq n), Which can be calculated by its complement P(X\leq n). For P(X\leq n), since n is big enough, we can use Central Limit Theorem to calculate out the approximation value of P(X\leq n); where n is 21.

\therefore P= (1-P)\left ( \sum_{i=1}^{120}Xi\leq 20 \right )

Xi be independent random variable such that P(Xi=1)=P