The mixed number 66 and two-thirds is 200 over 3, or 200/3, as a fraction. To convert a mixed number into a fraction, manipulate the whole number so that it shares a common denominator with the fractional component, and then add the two together.
All numbers can be written as a numerator over denominator. A whole number of 66 is simply a fraction with 66 as the numerator and one as the denominator. Multiply the top and bottom by 3 in order to obtain a common denominator with 2/3. Adding 198 over 3 and 2 over 3 yields a final fraction of 200 over 3.