Is this honestly a joke. How on earth could you expect a student to come up with an answer to a question with no information even slightly relevant to the answer; that is not a basis to judge math skills.

Also your above calculation is no better than the ones the grade eights had made. If you had any knowledge of farms you would know that the Shepard probably bought a lot of sheep too and maybe some of them belonged to his father. How can you assume that he started at 18. In Arabia some kids become Shepards at the age of 13.

Your example was just plain stupid and so is your assumption that they have bad math skills.