Question

On my homework 204\306 and 56:84 is equal to 2\3 but only one can be equal to 2\3

Answer 1

Why can only one of them be equal to  2/3 ? ? ?

For any fraction you name, there are an infinite number of other fractions
that have the same value.  That's why sometimes you're asked to 'simplify'
a fraction, or 'reduce it to lowest terms'.  The fraction you start with and the
fraction you end up with both have exactly the same value (if you do it correctly) . . . .
they are  EQUAL ! !

-- If you simplify  204/306 , you get  2/3 .

-- If you reduce  56 / 84  to lowest terms, you get  2/3 .

-- All three of those fractions have the same value.

--       204/306 ,  56 / 84 ,  and  2/3  are all  EQUAL .

If your big brother eats  204/306  of a pizza, and your little sister eats 
2/3  of another pizza, and you eat  56/84  of a pizza, each of you eats
the same amount !

Answer 2

Nothing in math rules states that. there can be any no. of equivalents to 2/3.