19 Four discs, each of radius 1 cm, are cut from a 5 cm by 5 cm cardboard square. Use the value 3.14 for a to find the area of cardboard left over. 20 One litre of water is poured into a rectangular...

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Extracted text: 19 Four discs, each of radius 1 cm, are cut from a 5 cm by 5 cm cardboard square. Use the value 3.14 for a to find the area of cardboard left over. 20 One litre of water is poured into a rectangular container. Find the height that the water will rise if the area of the base of the container is 80 cm2.