Two-thirds is 0.667 when rounded to three decimal places in decimal format. In actuality, the decimal representation of 2/3 is 0.66… Six is followed by an ellipsis to imply that its repetition is infinite.
The denominator must be changed to 10 to convert a fraction to decimal format. The denominator in the above case is three. When rounded to three decimal places, it is multiplied by 3.333 in order to reach ten. In order to convert 2/3 to a decimal, multiply two and three by 3.333. Three multiplied by 3.333 yields 10, but two multiplied by 3.333 yields 6.667 when rounded to three decimal places. The fraction thus becomes 6.667/10. Dividing 6.667 by 10 produces 0.667.