Four hundred ninety thousandths in decimals is 0.490
12.873 = twelve and eight hundred seventy-three thousandths.
305/1000 = 0.305, unless you meant three hundred and five thousandths, which would be 300.005
three hundred ninety-one thousandths . . . 0.391four tenths . . . 0.4The sum of (three hundred ninety-one thousandths) + (four tenths) = 0.791
You cannot write it as it appears.
It is forty three and seven hundred twenty nine thousandths.