What is the sum of 2 1/3, 3 5/6 and 6 2/3

2 1/3 + 3 5/6 + 6 2/3   = 12 5/6

Convert mixed fractions into fractions:

2 1/3 = (2*3 + 1)/3 = 7/3
3 5/6 = (3*6 + 5)/6 = 23/6
6 2/3 = (6*3 + 2)/3 = 20/3

Fractions must have the same denominator to be added or subtracted.
6 is the common multiple between 6 and 3. So numbers must be multiplied to the fraction to get a product of 6 in the denominator.

7/3 *  2/2 = 14/6
20/3 * 2/2 = 40/6

14/6 + 23/6 + 40/6 = (14+23+40)/6 = 77/6 = 12 5/6

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