Here's the problem:

If X horses can eat through Y bags of feed in Z days. How many days would U bags of feed last with V similar horses eating at the same rate?

My answer:

Let the number of days be a = U/V

The rate of eating for each horse is Y/X per day

V similar horses would consume V(Y/X) of bags per day

Therefore it would take U/V(Y/X) days

Now my teacher corrected this by putting (UX/VY)Z which I do not understand. Could someone explain this very clearly? With many thanks...