How do you write 0.4 as a fraction?

0.4 in fraction form is ##2/5##.

the place value of 0.4 is tenths, so when converted to a fraction, we have ##0.4*(100/100)## where ##100/100## is just equal to 1 so the equality of the equation is preserved; simplifying the fraction, we get ##0.4*(100/100)=40/100=4/10=2/5##.