To find which fraction is equal to 0.40, we first need to convert it into a fraction not in simplest form. Since the decimal 0.40 is equal to 0.4 (you can add any zero to the right of a decimal without changing the value), we can now convert 0.4 into a fraction. Since 0.4 has 4 in the tenths place, 0.4 = 4/10. Now we can simplify. To simplify, we need to find the GCF of the numerator and the denominator. The GCF of 4 and 10 is 2. Now we can remove 2 from both the numerator and denominator. The fraction then becomes:
(4/2)/(10/2)
Which simplifies to our answer of:
2/5