Final answer:
The water level for the three-month period is less than the yearly average. The three-month period water level is -23/16 inches, while the yearly average is -61/48 inches.
Step-by-step explanation:
The water level for the three-month period is less than the yearly average. Let's calculate the yearly average water level by adding up the water levels for each month, and then dividing by the number of months. The water levels for June, July, and August are -2 1/8, 1 1/4, and -9/16 inches respectively.
To add and subtract the mixed numbers, we need to convert them into improper fractions. The average is calculated as (-17/8 + 5/4 - 9/16) / 3, which simplifies to -61/16 / 3. Dividing the numerator and denominator by 3, we get -61/48. Therefore, the yearly average water level is -61/48 inches. Comparing this to the three-month period water level, which is -2 1/8 + 1 1/4 - 9/16 inches, we need to find a common denominator and then subtract the fractions.
The common denominator is 8. Converting the mixed numbers to improper fractions, the three-month period water level is (-17/8 + 10/8 - 9/16) inches. Simplifying, we get -17/8 + 10/8 - 9/16 = -34/16 + 20/16 - 9/16 = -23/16 inches. Since -23/16 is less than -61/48, the water level for the three-month period is less than the yearly average.