3.400

One-thousand (1,000) thousandths is equal to one (1), so three-thousand (3,000) thousandths is equal to 3, which is a whole number and is on the left side of the decimal. Four-hundred (400) thousandths is a fraction that is also equal to forty (40) hundredths or four (4) tenths, so the four is on the right side of the decimal. The two extra zeros show that it should be read as 400 thousandths rather than 4 tenths.

If you had asked how to write three thousand AND four-hundred thousandths, the answer would be 3,000.400. The decimal is read as "and".

One-thousand (1,000) thousandths is equal to one (1), so three-thousand (3,000) thousandths is equal to 3, which is a whole number and is on the left side of the decimal. Four-hundred (400) thousandths is a fraction that is also equal to forty (40) hundredths or four (4) tenths, so the four is on the right side of the decimal. The two extra zeros show that it should be read as 400 thousandths rather than 4 tenths.

If you had asked how to write three thousand AND four-hundred thousandths, the answer would be 3,000.400. The decimal is read as "and".