ab=10 means that aXb is 10, similarly aXc is 5. If your answers can only be whole numbers then--- if aXc =5, then a and c can only be 5 or 1 since that is the only factorization of 5---- if a =1, then b =10 and c=5. If a=5, then b=2 and c =1. If fractions can be included and negative numbers can be included, there are other possibilities. But in either case, ac is 5.