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Question
A quadrilateral has three acute angles each measures 80°. What is the measure of the fourth angle?
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Solution
\[\text{ Let x be the fourth angle } . \]
\[ \text{ Since, the sum of all angles of a quadrilateral is } 360°, \text{ we have: } \]
\[80° + 80° + 80° + x = 360° \]
\[ \Rightarrow 240° + x = 360° \]
\[ \Rightarrow x = 120° \]
\[ \therefore \text{ The fourth angle is } 120° .\]
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