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For the binomial distribution table of defective tomatoes taken over $x=0$ to $5$, the mean and standard deviation are:
A2.5662 and 1.4620
B2.4454 and 1.5131
C2.5662 and 1.5969
D3.0000 and 1.5969
Answer & Solution
Correct answer: A. 2.5662 and 1.4620
1. The table is truncated at $x=5$, so the mean must be computed from it directly, not from $np$.
2. Apply $E(X)=\sum x_i p(x_i)$ across $x=0$ to $5$, giving $2.5662$.
3. For the spread use $\delta=\sqrt{E(X^2)-[E(X)]^2}$.
4. That evaluates to $1.4620$.
5. Using $E(X)=np=3$ and $\delta=npq=1.5969$ ignores the truncation and is the common error; $2.4454$ and $1.5131$ belong to the Poisson table.
_Source: NECTA ACSEE 2023 Advanced Mathematics 142/2, Question 1: Probability_
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