Answer:
a) The confidence interval is 
.
Step-by-step explanation:
We have to calculate a confidence interval (CI) of a difference of proportions.
For the existing procedure, the proportion is:
For the new procedure, the proportion is:
To calculate the CI, we need to estimate the standard deviation
For a 90% CI, the z-value is 1.64.
Then, the CI is:
It has to do with the unit circle, I think it is A because it should be 2(0+ (-1)) but I would probably wait for someone to come behind me and explain it better sorry couldn't help more
Answer:
1877 computer users
Step-by-step explanation:
We have that for 95% of confident, the value of z has a value of 1.96 (attached table about it), they also mention the margin of error (E) that is 10 and finally the standard deviation (sd) that has a value of 221.
We apply the following formula:
n = [z * sd / E] ^ 2
replacing:
n = [1.96 * 221/10] ^ 2
n = 1876.27
that is, the minimum sample size is 1877
During week 2, he could type 15 words per minute, at his fourth week, he could type 30. So 30-15=15. He could type 15 words faster on week 4 than he could at week 2.
