If you mean 1.421 plus 3.004 then it is 4.425
It is not clear whether you mean 3 (hundred thousandths) = 3*10^-5or(3 hundred) thousandths = 3*10^-1.
eight hundred and forty thousandths
Look at the digist in the ten-thousandths place. If it is 5 or greater, round the digist in thousandths place to the next higher number. If it is less than five, leave the digit in thousandths place as it is. In the case of 7.8298, rounding it to thousandths means the 9 will be a 0 and the 2 in hundredths place would change to a 3. It will be 7.830.
3 and 87 thousandths.
8.315
2.514 + 1.003 = 3.517
Because 17 thousandths is three places to the right of the decimal and well, 3 is more than 2.
If you mean 1.421 plus 3.004 then it is 4.425
3 Thousandths = .003 3.995 - .003 = 3.992
I know because 17 thousandths is 3 places after the decimal.
17 being a whole number lies to the left of the point. To turn it into thousandths you have to move it to the right, three places. One is 1.7, 2 is 0.17, 3 is 0.017, The thousandths POSITION is 0.001. So 17 thousandths does not lie more than two places to the right of that. It does lie more than two places to the right of the decimal point. Don't mix up these. There is no such thing as the "thousandths decimal point".
5.872
7.765-0.003 = 7.762
5.889 - 0.003 = 5.886
30 thousandths = 3 hundredths = 0.030 = 3/100 or, if you meant 3 ten thousandths, 3 ten thousandths = 0.0003 = 3/10000
2.345