A fraction represents a part of a whole.

**Answer: 0.4 can be written in a fraction as 4/10 or 2/5.**

**Explanation:**

To begin, we must first remove the decimal.

Because there is just one digit following the decimal, we multiply and divide by ten.

0.4/1 x 10/10 = 4/10 is the result.

The result of 4/10 can be further reduced to 2/5.