A tank contained some water at first. At 7 a.m., Tap A was turned on to fill the tank. At 9 a.m., Tap B was also turned on to fill the tank. The graph below shows the volume of water in the tank over 4 hours.What was the amount of water filled by Tap B between 9 a.m. and 11 a.m.? (2 marks)
Answer: 120 litres
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5 gaps → 50 1 gap → 50 ÷ 5 = 10
7 am → 40 litres 9 am → 100 litres
tap A in 2 hours → 100 - 40 = 60 litres
11 am → 280 litres
tap A + B in 2 hours (9 to 11) → 280 - 100 = 180 litres
difference (in 2 hours) → 180 - 60 = 120 litres
which is also what tap B has filled