or
or
Two-thirds of the mangoes... rotten.
Use the same rule for fractions as for percent's -
If it's a fraction of a plural, countable noun = plural
If it's a fraction of a singular noun = singular
If it's a faction of a uncountable noun = singular
Example:
Two Thirds of the mangoes are rotten.
Two Thirds of the mango is eaten.
Two thirds of the money is spent. (un-count noun)
