4) a) Suppose \( X_{n} \xrightarrow{P} X \) and \( a \) is a constant. Prove that \( a X_{n} \xrightarrow{P} a X \).
b) If \( T_{n}=\sum_{i=1}^{n} X_{i} \) is the sum of a random sample of size \( n \) with mean \( \mu \) and variance \( \sigma^{2} \), show that \( T_{n} \approx A N\left(n \mu, n \sigma^{2}\right) \).
c) Let \( X_{i}, i=1,2, \ldots, n \) be independent Bemoulli trials with a success probability \( p \), and let \( Y_{n}=\frac{1}{n} \sum_{i=1}^{n} X_{i} \)
(i) Show that \( \sqrt{n}\left(Y_{n}-p\right) \xrightarrow{D} N(0, p(1-p)) \). Clearly state theorem(s) used in the proof.
(ii) A college knows from past experience that only \( 30 \% \) of students admitted to first year courses will actually attend classes. If 450 were admitted in a certain year, approximate the probability that more than 150 students actually attend the class.
[State the assumptions and conditions checked when applying the approximation].