# Clinical trial tests a method designed to increase the probability of conceiving a girl. In the study, 340 babies were born, and 289 of them were girls. Use the sample data to construct a 99% confidence interval estimate of the percentage of girls born?

##
.........< p <..........born?

.........< p <..........born?

##### 1 Answer

We are 99% confident that the true proportion of female babies is captured by the interval from

#### Explanation:

We want to estimate the proportion of female babies born.

We can use a one-proportion

- Random: We must assume that the study uses a random sample of some population of babies born.
- Independence/10% condition: We must assume that there are more than
#340*10 = 3400 " babies"# in the sample. - Large/Normal: We must check that both
#(hatp)(n)# and#(1- hatp)(n)# are greater than or equal to 10:

#(hatp)(n) = (.85)(340)=289 >=10#

#(1- hatp)(n) = (1-.85)(340) = 51 >=10#

The equation for a one-proportion z-interval is:

Use the table of standard normal probabilities to find

To find

We get:

Substitute values into the formula:

Confidence interval:

We are 99% confident that the true proportion of female babies is captured by the interval from