91影视

Mean,$渭=0.69$

Standard deviation,$蟽=0.16$

The formula used:$z=\frac{x鈭�渭}{蟽}$

The $Xth$ percentile represents a data value with $x$ percent of the data values below it.

That implies

The $60th$ percentile represents a data value with $60\%$ of the data values below it.

Now,

In the normal probability table of the appendix, find the $z-$score that corresponds to a probability of $60\%$ (or $0.60$).

Note that

The probability that comes closest is $0.5987$ which is in row $0.2$ and column$.05$ of the normal distribution.

probability table.

Then

The corresponding $z鈭�$ score,

$z=0.25$

In order to find $nth$ percentile, calculate the $z鈭�$ score

$z=\frac{x鈭�渭}{蟽}=\frac{x鈭�0.69}{0.16}$

Equate the above two expressions:

$\frac{x鈭�0.69}{0.16}=0.25$

Multiply both sides by $0.16$:

$x鈭�0.69=0.04$

Add $0.69$ to both sides:

$x鈭�0.69+0.69=0.04+0.69$

That becomes

$x=0.73$

Thus,

$60th$the percentile will be $0.73$ ounces.

Calculate the Z 鈭� score,

$z=\frac{x鈭�渭}{蟽}=\frac{1鈭�0.69}{0.16}鈮�1.94$

To find the equivalent probability, use the normal probability table in the appendix.

The usual normal probability table for $P(z<鈭�1.79)$has a row that starts with $1.9$and a column that starts with$.04$

$$\begin{gathered} P(x>0.1)=P(z>1.94) \\ =1鈭�P(z<1.94) \\ =1鈭�0.9738 \\ =0.0262 \end{gathered}$$

Therefore,

Around $0.0262$ of the first$鈭�$ class letters at this post off ice require extra postage.