99% confidence interval = [-35.47,-26.53]
Step-by-step explanation:
For Method 1:
For Method 2:
We need to find the 99% confidence interval for the true difference between testing averages for students using Method 1 and students using Method 2.
Step 1: Find the point estimate for the true difference between the population means.
Therefore the point estimate for the true difference between the population means is -31.
Step 2: Find margin of error at 99% confidence.
From the standard normal table the critical value of z at 99% confidence = 2.576.
The formula for margin of error:
Substitute the values.
Therefore, the margin of error is 4.47.
Step 3: Find 99% confidence interval.
Therefore, the 99% confidence interval is [-35.47,-26.53].
7 or more hours
15 + 15 is 30