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Question Puzzle: I am an acute angle. If you double my measure, you get an acute angle. If you triple my measure, you will get an acute angle again. If you quadruple (four times) my measure, you will get an acute angle yet again! But if you multiply my measure by 5, you will get an obtuse angle measure. What are the possibilities for my measure?
Let the measure of the angle be m
Then 5 × m > 90 but 4 × m < 90
or m > \(\frac{90}{5}\) and m < \(\frac{90}{4}\)
Hence m > 18 but m < 22 ½
Hence measure of the angle is 19° or 20° or 21°