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Puzzle of the Day

These puzzles are also printed in Eight days a week, a booklet published by the Association of Teachers of Mathematics.The Association of Teachers of Mathematics

To change a temperature from degrees Celsius to Fahrenheit you can multiply by 9, divide by 5 then add 32. An approximate method is to simply double and add 30. For what range of temperatures is the approximate method within one degree of the accurate method?

Answer: between 5 and 15

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