Justify use of normal approximation

A question is this type if and only if it explicitly asks to justify or explain why the normal approximation to Poisson is appropriate, typically requiring λ ≥ 10 or similar condition.

1 questions

OCR S2 2009 June Q2

2 The random variable \(D\) has the distribution \(\operatorname { Po } ( 20 )\). Using an appropriate approximation, which should be justified, calculate \(\mathrm { P } ( D \geqslant 25 )\).