Fill the 13 oz bottle, from it fill the 5 oz bottle and pour the remaining 8 oz from the 13 oz bottle into the 11 oz bottle.  Return the 5 oz from the 5 oz bottle to the medicine bottle and fill the 13 oz bottle again.  Once you have, again, poured 5 oz from the 13 oz bottle into the 5 oz bottle and have restored it again to the medicine bottle you have an 8 oz servings in each of the medicine bottle, the 11 oz bottle and the 13 oz bottle.

ent (eight, nine, ten)