Lanjutan Contoh Soal 2 Distribusi Normal

 $\begin{array}{ll}\\ 6.&\textrm{Luas daerah yang diarsir di bawah}\\ &\textrm{kurva normal baku berikut adalah}\:  ....\\ &\textrm{a}.\quad 0,4861\\ &\textrm{b}.\quad \color{red}0,4878\\&\textrm{c}.\quad 0,4881\\ &\textrm{d}.\quad 0,4938\\ &\textrm{e}.\quad 0,4946\\\\   \end{array}$.

$.\qquad\begin{aligned}&\textbf{Jawab}:\\ &\textrm{Perhatikan tabel}\: \color{blue}\textrm{distribusi normal}\:  \color{black}\textrm{berikut}\\&\begin{array}{|c|c|c|c|c|c|c|c|c|c|c|}\hline \textrm{z} &0&1&2&3&4&5&6&7&8&9\\\hline \vdots &&&&&&\downarrow &&&&\\ \vdots &&&&&&&&&&\\ 2,2 &&&&&&\color{red}0,4878&&&&\\ \vdots &&&&&&&&&&\\\hline \end{array}\\ &\textrm{Sehingga nilai}\: \: \textrm{z}=2,25\: \: \textrm{luasnya}=0,4878 \end{aligned}$.

$\begin{array}{ll}\\ 7.&\textrm{Luas daerah yang diarsir di bawah}\\ &\textrm{kurva normal baku berikut adalah}\:  ....\\ &\textrm{a}.\quad \color{red}0,1138\\ &\textrm{b}.\quad 0,3810\\&\textrm{c}.\quad 0,3862\\ &\textrm{d}.\quad 0,4948\\ &\textrm{e}.\quad 0,5000\\\\   \end{array}$.
$.\qquad\begin{aligned}&\textbf{Jawab}:\\ &\textrm{Perhatikan tabel}\: \color{blue}\textrm{distribusi normal}\:  \color{black}\textrm{berikut}\\&\begin{array}{|c|c|c|c|c|c|c|c|c|c|c|}\hline \textrm{z} &0&1&2&3&4&5&6&7&8&9\\\hline \vdots &&&&&&&\downarrow &&\downarrow&\\ \vdots &&&&&&&&&&\\ 1,1 &&&&&&&\downarrow&&\color{red}0,3810&\\ \vdots &&&&&&&&&&\\ 2,5&&&&&&&\color{red}0,4948&&&\\ \vdots &&&&&&&&&&\\\hline \end{array}\\ &\textrm{Sehingga nilai}\: \: \textrm{z}=1,18\: \: \textrm{luasnya}=0,3810\\ &\textrm{Dan nilai}\: \: \textrm{z}=2,56\: \: \textrm{luasnya}=0,4948\\ &\textrm{maka luas arsiran}\\ &=P(1,18<Z<2,56)\\ &=P(0<Z<2,56)-P(0<Z<1,18)\\ &=0,4948-0,3810\\ &=\color{red}0,1138 \end{aligned}$.

$\begin{array}{ll}\\ 8.&\textrm{Luas daerah yang diarsir pada gambar}\\ &\textrm{di bawah adalah 0,9332, maka nilai}\: \: \textrm{z}=\:  ....\\    \end{array}$.
$.\qquad\begin{array}{ll}\\ &\textrm{a}.\quad 1,05\\ &\textrm{b}.\quad 1,06\\&\textrm{c}.\quad 1,16\\ &\textrm{d}.\quad \color{red}1,50\\ &\textrm{e}.\quad 1,60\\\\ &\textbf{Jawab}:\\ &\textrm{Luas arsiran adalah}\\ &=P(Z<z)=0,9332\\ &=\color{blue}0,5\color{black}+0,4332\\ &=0,5+P(0<Z<z)\\ &\textrm{lihat/konfirmasi ke tabel}\\ &\textrm{z}=\color{red}1,50\\ &\begin{aligned}&\textrm{Perhatikan tabel}\: \color{blue}\textrm{distribusi normal}\:  \color{black}\textrm{berikut}\\&\begin{array}{|c|c|c|c|c|c|c|c|c|c|c|}\hline \textrm{z} &0&1&2&3&4&5&6&7&8&9\\\hline \vdots &\downarrow &&&&&&&&&\\ \vdots &&&&&&&&&&\\ 1,5 &\color{red}0,4332&&&&&&&&&\\ \vdots &&&&&&&&&&\\\hline \end{array}\\ &\textrm{Sehingga luasnya}=0,4878,\: \: \textrm{batas z}=1,50  \end{aligned}    \end{array}$.

$\begin{array}{ll}\\ 9.&\textrm{Luas daerah yang diarsir pada gambar}\\ &\textrm{di bawah adalah}=\:  ....\\    \end{array}$.
$.\qquad\begin{array}{ll}\\ &\textrm{a}.\quad 0,9750\\ &\textrm{b}.\quad 0,5000\\&\textrm{c}.\quad 0,4750\\ &\textrm{d}.\quad \color{red}0,0250\\ &\textrm{e}.\quad 0,0200\\\\ &\textbf{Jawab}:\\ &\textrm{Luas arsiran adalah}\\ &=P(0\leq Z\leq \infty )-P(0\leq Z\leq 1,96)\\ &=\color{blue}0,5\color{black}-0,4750\\ &=\color{red}0,0250  \end{array}$.

$\begin{array}{ll}\\ 10.&\textrm{Misalkan tinggi siswa kelas XII berdistribusi}\\ &\textrm{normal dengan rata-rata 167,5 cm dengan}\\ &\textrm{simpangan baku 4,6 cm. Jika jumlah siswa}\\ &\textrm{yang diteliti sebanyak 10.000 siswa, maka }\\ &\textrm{jumlah siswa yang memiliki tinggi lebih}\\ &\textrm{dari 160 cm sebanyak}\: ....\\ &\textrm{a}.\quad 16.300\\ &\textrm{b}.\quad \color{red}9.484\\&\textrm{c}.\quad 5.516\\ &\textrm{d}.\quad 4.484\\ &\textrm{e}.\quad 4.474\\\\ &\textrm{Jawab}:\\ &\begin{aligned}&\textrm{Diketahui dari soal di atas}\\ &n=10.000,\: \mu =167,5\: \textrm{cm},\: \sigma =4,6\\ &z=\displaystyle \frac{x-\mu }{\sigma }=\displaystyle \frac{160-167,5}{4,6}=\color{red}-1,63\\ &\begin{aligned}P(X> 160)&=P(Z> -1,63)\\ &=P(0\leq Z\leq 1,63)\\ &\qquad\qquad+P(0\leq Z\leq \infty )\\ &=0,4484+0,5\\ &=0,9484 \end{aligned}\\ &\textrm{Sehingga total siswa yang dimaksud}\\ &\textrm{sebanyak}:0,9484\times 10.000=\color{red}9.484 \end{aligned}   \end{array}$.



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