The question is ambiguous. The answer is either 400.001 or 0.401. In each case, the 1 is in the third position after the decimal point.
Maybe I should be putting this in discussion, but I believe the word 'and', which may be used often when talking to say 'four hundred and one' to mean 401, is incorrect in this usage. I believe the correct verbage is 'four hundred one' to mean 401, so 'four hundred and one thousandths' would mean 400 and 1/1000.
13.400
One hundred one and four hundred eighty-seven thousandths.
three hundred ninety-one thousandths . . . 0.391four tenths . . . 0.4The sum of (three hundred ninety-one thousandths) + (four tenths) = 0.791
One and four hundred nine thousandths.
One hundred eighty-four thousandths.
Eighty-one and four hundred eighty-four thousandths in decimal notation is 81.484
One hundred four and three thousandths.
13.400
It is 0.401
0.0421
One hundred ninety-one and four hundred one thousandths.
One hundred four and sixteen thousandths (104.016) in standard form = 1.04016 × 102
One hundred one and four hundred eighty-seven thousandths.
Four thousand, two hundred one hundred-thousandths.
three hundred ninety-one thousandths . . . 0.391four tenths . . . 0.4The sum of (three hundred ninety-one thousandths) + (four tenths) = 0.791
One and seven hundred four thousandths.
Four and one hundred ninety-six thousandths.