I was teaching the Normal Distribution last night, including using it to approximate the Binomial Distribution. As usual, students have difficulties with the following:
(a) knowing the difference between Var (X1 + X2 + X3) and Var (3X), and knowing WHEN the question refers to which;
(b) doing continuity correction for P(X> k) or P(X < k) when X is a discrete variable and there is a need to approximate its distribution to Normal.
I suggest students read their H2 Math textbook carefully and thoroughly, if their own JC notes are inadequate. As you know, in Math, mistakes done at the START of the working will most likely cost you ALL the marks even if your answer is one page long. : )
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