Write 0.4 as a fraction.
Understand the Problem
The question is asking to convert the decimal number 0.4 into a fraction. This involves identifying the place value of the decimal and expressing it as a fraction with a numerator and denominator.
Answer
The fraction equivalent of the decimal 0.4 is $\frac{2}{5}$.
Answer for screen readers
The fraction equivalent of the decimal 0.4 is $\frac{2}{5}$.
Steps to Solve

Identify the Decimal Place Value
The decimal 0.4 is in the tenths place, which means it can be expressed as $\frac{4}{10}$ (4 tenths). 
Simplify the Fraction
To simplify $\frac{4}{10}$, we need to find the greatest common divisor (GCD) of 4 and 10, which is 2. We divide both the numerator and the denominator by 2.
$$ \frac{4 \div 2}{10 \div 2} = \frac{2}{5} $$ 
Final Result
Thus, the simplest form of the fraction representing the decimal 0.4 is $\frac{2}{5}$.
The fraction equivalent of the decimal 0.4 is $\frac{2}{5}$.
More Information
Converting decimals to fractions is a useful skill in mathematics, especially in properties involving ratios, percentages, and more. Remember that decimals terminating in a specific digit can always be turned into fractions by using their corresponding place value.
Tips
 A common mistake is forgetting to simplify the fraction after converting it from decimal to fraction. Always check if the fraction can be reduced!