Given data:
Mean: 993mL
Standard deviation: 7mL
Find p(988
1. Find the z-value corresponding to (x>988), use the next formula:

2. Find the z-value corresponding to (x<991):

3. Use a z score table to find the corresponding values for the z-scores above:
For z=-0.71: 0.2389
For x=-0.29: 0.3859
4. Subtract the lower limit value (0.2389) from the upper limit value (0.3859):

5. Multiply by 100 to get the percentage:

Then, 14.7% of the bottles have volumes between 988mL and 991mL