Contoh Soal 3 Distribusi Normal

 $\begin{array}{l}\\ 11.& \text{Tersiar kabar bahwa harga beras di pasar di}\\ & \text{wilayah B adalah}\text{Rp}8.000,00/\text{Kg dengan}\\ & \text{simpangan baku}\text{Rp}1.500,00.\text{Berdasar kabar}\\ & \text{tersebut dilakukan penelitian dengan mengambil}\\ & \text{sampel secara acak sebanyak}60\text{kios yang dan}\\ & \text{diperoleh rata-rata harga beras}\text{Rp}7.800,00/\text{Kg}\\ & \text{Jika penghitungan menggunakan tingkat}\\ & \text{signifikansi}5\mathrm{\%},\text{maka kesimpulan berikut }\\ & \text{yang tepat adalah}....\\ & \text{a}.\text{harga beras di pasar lebih dari}\text{Rp}7.800,00/\text{Kg}\\ & \text{b}.\text{harga beras di pasar lebih dari}\text{Rp}8.000,00/\text{Kg}\\ & \text{c}.\text{harga beras di pasar kurang dari}\text{Rp}0.000,00/\text{Kg}\\ & \text{d}.\text{harga beras di pasar}\text{Rp}7.800,00/\text{Kg}\\ & \text{e}.\text{harga beras di pasar}\text{Rp}8.000,00/\text{Kg}\\ \\ & \mathbf{\text{Jawab}}:\mathbf{\text{e}}\\ & \begin{array}{rl}& \underset{―}{\text{Hipotesis}}\\ & \text{Rata-rata harga beras dipasar}\text{Rp}8.000,00/\text{Kg}\\ & {\text{H}}_0:\mu =8.000\\ & {\text{H}}_0:\mu \ne 8.000\\ & \underset{―}{\text{Daerah Kritis}}\\ & \text{Taraf nyata yang dipilih adalah}=\alpha =0,05=5\mathrm{\%}\\ & {\displaystyle \frac{\alpha }{2}=2,5\mathrm{\%}=0,025}\\ & {\text{z}}_{0,025}=1,96\\ & \text{maka daerah kritis/penolakannya adalah}\\ & \text{z}<-1,96\text{atau}\text{z}>1,96\end{array}\end{array}$.

$.\begin{array}{rl}& \underset{―}{\text{Nilai Satistik Uji}}\\ & \text{Dihitung dengan rumus}:\text{z}={\displaystyle \frac{\bar{\text{x}}-{\mu }_0}{{\displaystyle \frac{\sigma }{\sqrt{n}}}}}\\ & \text{z}={\displaystyle \frac{7.800-8.000}{{\displaystyle \frac{1.500}{\sqrt{60}}}}=-{\displaystyle \frac{200\sqrt{60}}{1.500}=-1,03}}\\ & \underset{―}{\text{Keputusan Uji}}\\ & \text{Karena nilai}-1,96<\text{z}<1,96,\\ & \text{maka}{\text{H}}_0\text{diterima}\\ & \underset{―}{\text{Kesimpulan}}\\ & \text{Rata-rata harga beras dipasar}\text{Rp}8.000,00/\text{Kg}\end{array}$ .