A random sample of two observations $$\(X_{1}\)$$ and $$\(X_{2}\)$$ is taken from a population with unknown mean $$\(\mu\)$$ and unknown variance $$\(\sigma^{2}\)$$ Explain what you understand by an unbiased estimator for $$\(\mu\)$$ (1) Two estimators for $$\(\mu\)$$ are $$\(U_{1}\)$$ and $$\(U_{2}\)$$ where $$\[ U_{1}=3 X_{1}-2 X_{2} \quad \text { and } \quad U_{2}=\frac{X_{1}+3 X_{2}}{4} \]$$

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