Final answer:
Mrs. Singh's class of 18 students will use approximately 4.75 gallons of water when each student fills their 1-liter water bottle once.
Step-by-step explanation:
When Mrs. Singh's 18 students fill their 1-liter water bottles once each, the total amount of water used will be the sum of the volume of all bottles. Since each bottle holds 1 liter of water, the class will use a total of 18 liters of water. To convert this volume into gallons, we use the conversion factor that 1 gallon is approximately 3.79 liters.
Step 1: Calculate the total volume of water in liters.
18 students × 1 liter/student = 18 liters
Step 2: Convert liters to gallons using the conversion factor.
18 liters ÷ 3.79 liters/gallon ≈ 4.75 gallons
Therefore, the class will use approximately 4.75 gallons of water.