To evaluate the expression \( 0.4 - 0.2 + 0.8 + (-0.8) \), we can follow these steps:
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Start with the first two terms: \[ 0.4 - 0.2 = 0.2 \]
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Now, add the next term: \[ 0.2 + 0.8 = 1.0 \]
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Now, add the last term: \[ 1.0 + (-0.8) = 1.0 - 0.8 = 0.2 \]
Thus, the value of the expression \( 0.4 - 0.2 + 0.8 + (-0.8) \) is \( \boxed{0.2} \).