8: Advanced Proportional - Proportions and Ratios

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The tank is four-fifths full. Andrew will use two thirds of that water to water his plants, 200 litres. How much water does the tank hold when full?

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Student: One third of the water would be one hundred litres. One third of four fifths is four fifteenths. If four fifteenths of the tank is one hundred litres one fifteenth is twenty-five litres. Fifteen times twenty-five equals three hundred and seventy-five litres.

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Students at the Advanced Proportional stage are learning to select from a repertoire of part-whole strategies to solve and estimate the answers to problems involving fractions, proportions, and ratios. These strategies are based on finding common factors and include strategies for the multiplication of decimals and the calculation of percentages.