Respuesta :
Given:
Sample size = 100
p = 30% = 0.30
p' = 25% = 0.25
Let's find the probability that a sample proportion will over- or under-estimate the parameter by more than 5%.
Here, the error is:
Errror = |p' - p| = |0.25 - 0.30| = |-0.05| = 0.05
This error is not surprising.
Now, apply the formula:
[tex]\begin{gathered} \sigma p^{\prime}=\sqrt{\frac{p(1-p)}{n}} \\ \\ \sigma p^{\prime}=\sqrt{\frac{0.3(1-0.3)}{100}} \\ \\ \sigma p^{\prime}=\sqrt{\frac{0.3(0.7)}{100}}=\sqrt{\frac{0.21}{100}}=\sqrt{0.0021}=0.0458 \end{gathered}[/tex]Now, to find the probability that a sample proportion will be over or underestimate more than 5% will be:
[tex]\begin{gathered} p(p^{\prime}<0.3-0.05)+p(p^{\prime}>0.3+0.05) \\ \\ p(p^{\prime}<0.25)+p(p^{\prime}>0.35) \\ \\ z=\frac{p^{\prime}-\mu p^{\prime}}{\sigma p} \\ \\ Where:\mu p^{\prime}=0.3 \\ \end{gathered}[/tex]Hence, we have:
[tex]\begin{gathered} p(z<\frac{0.25-0.3}{0.0458})+p(z>\frac{0.35-0.3}{0.0458}) \\ \\ p(z<\frac{-0.05}{0.0458})+p(z>\frac{0.05}{0.0458}) \\ \\ p(z<-1.09)+p(z>1.09) \end{gathered}[/tex]Using the standard normal distribution table, we have:
NORMSDIST(-1.09) =0.1379
NORMSDIST(1.09) = 0.8621
Hence, we have:
p(z<-1.09) = 0.1379
p(z>1.09) = 1 - 0.8621 = 0.1379
p(z<-1.09) + p(z>1.09) = 0.1379 + 0.1379 = 0.2758
Therefore, the probability is 0.2758.
ANSWER:
0.2758