To multiply \(-\frac{2}{5}\) by \(\frac{3}{10}\), we can use the rules for multiplying signed numbers and multiply the fractions directly.
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Multiply the numerators: \[ -2 \times 3 = -6 \]
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Multiply the denominators: \[ 5 \times 10 = 50 \]
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Combine the results: \[ -\frac{6}{50} \]
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Simplify the fraction: The greatest common divisor (GCD) of 6 and 50 is 2. We can simplify: \[ -\frac{6 \div 2}{50 \div 2} = -\frac{3}{25} \]
So the answer in simplest form is: \[ \boxed{-\frac{3}{25}} \]