What is 0.4 in its standard form ? ?

To get the answer you need to move the decimal to the right until it is behind the first number that isn't a zero. then you count how many spaces you moved the decimal which will make the number you will square 10 by. to know if the power is negative or positive that depends on the direction you move the decimal. since you would move it to the right that would make it a negative.
4x10^-5