To simplify the expression \( 24 \div 2^3 - 4 \cdot 5 \), we will follow the Order of Operations (PEMDAS/BODMAS).
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Exponents: Calculate \( 2^3 \). \[ 2^3 = 8 \]
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Division: Next, perform the division \( 24 \div 8 \). \[ 24 \div 8 = 3 \]
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Multiplication: Now handle the multiplication \( 4 \cdot 5 \). \[ 4 \cdot 5 = 20 \]
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Subtraction: Finally, subtract the results: \( 3 - 20 \). \[ 3 - 20 = -17 \]
So, the simplified expression yields: \[ \boxed{-17} \]