A farmer uses a knapsack sprayer with a tank capacity of 15 litres. If the sprayer delivers 0.5 litres per minute and the farmer works for 4 hours without refilling, how many times must the tank be refilled?

Total volume sprayed = 0.5 L/min × 240 min = 120 litres. Number of tank loads needed = 120 ÷ 15 = 8 loads. Since the first load is already in the tank at the start, the number of refills = 8 − 1 = 7 times. Distractors arise from forgetting to subtract the initial fill or miscalculating total volume.