Answer:
Approximately [tex]0.157[/tex].
Step-by-step explanation:
Let [tex]X[/tex] denote the speed of a car. The question is asking for [tex]P(60 \le X \le 70)[/tex].
That probability is equal to [tex]P(X \le 70)- P(X \le 60)[/tex].
Find each of [tex]P(X \le 60)[/tex] and [tex]P(X \le 70)[/tex] using a [tex]Z[/tex]-table.
Calculate the [tex]Z[/tex] value for [tex]x = 70[/tex] and [tex]x = 60[/tex]:
At [tex]x = 70[/tex], [tex]\displaystyle z = \frac{x - \mu}{\sigma} = \frac{60 - 55}{5} = 3[/tex].
At [tex]x = 60[/tex], [tex]\displaystyle z = \frac{x - \mu}{\sigma} = \frac{70 - 55}{5} = 1[/tex].
In other words: [tex]P(X \le 70) = P(Z \le 3)[/tex] whereas [tex]P(X \le 60) = P(Z \le 1)[/tex].
Look up [tex]P(Z \le 3)[/tex] and [tex]P(Z \le 1)[/tex] on a [tex]Z[/tex]-table. The question is asking that the answer be rounded to the nearest thousandth. Therefore, keep at least more decimal places than that in intermediate values.
[tex]P(Z \le 3) \approx 0.9987[/tex] and [tex]P(Z \le 1) \approx 0.8413[/tex].
Therefore:
[tex]\begin{aligned}P(60 \le X \le 70) &= P(X \le 70)- P(X \le 60) \\ &= P(Z \le 3) - P(Z \le 1) \approx 0.157\end{aligned}[/tex].
