Step 1:

(27a)

Total number of Danish cell phone users in the survey are $\"\"$ .

The probability of phone users suffered from brain cancer or nervous system $\"\"$ .

Definition of specific confidence interval for a proportion : $\"\"$ ,

where $\"\"$ is the population proportion.

$\"image\"$ is the sample proportion.

$\"image\"$ .

n is the sample size.

$\"\"$ is the confidence interval.

Step 2:

$\"image\"$ for 90 % confidence interval is 1.65.

$\"\"$ .

90% of confidence interval for the proportion is

$\"\"$

90% of confidence interval for the proportion of 0.0321% Danish phone users suffered from brain cancer or nervous system is $\"\"$

Step 3:

No, it doesn’t appear that cell phone users have a different cancer rate. Since the 90% confidence interval based on the sample includes the percentage(0.0340%) from the survey taken prior to cell phone use.

Solution:

(27 a)

90% of confidence interval for the proportion of 0.0321% Danish phone users suffered from brain cancer or nervous system is $\"\"$

(27 b)