math
posted by ALex .
Alex has 1/2 pizza left in the fridge. At breakfast he ate 1/3 of it. What fraction of the original pizza does he have left?

Your second sentence is not clear.
"At breakfast he ate 1/3 of it"
1/3 of the pizza he has left, or 1/3 of the original pizza ?
If he eats 1/3 of what is left in the fridge, then (2/3) of the half  pizza is left, or 1/3 of the pizza is left
if he eats 1/3 of the original pizza for breakfast then he has eaten
1/2 + 1/3 = 5/6 , leaving 1/6 of the pizza