How do we write 0.040 as a fraction?

To write 0.040 as a fraction, we first identify the decimal place value of each digit. In this case, the zero after the decimal point is in the thousandths place. Therefore, 0.040 can be written as 40/1000. To simplify this fraction, we divide the numerator and denominator by their greatest common factor, which is 10 in this case. Thus, 0.040 can be simplified to 4/100.