Guest petr. yes, you are missing the fact that it was a discussion between to mathematicians, so each could be expected to understand the logical processes. So, once the product of the three ages had been set at 36, the total of the ages was equal to the number of tables in the restaurant. The other mathematician was still unable to solve this, and so the idea of three numbers with a product of 36, and a sum of "X" had to have more than 1 solution. Once we have found all the sets of 3 digits with a product of 36, we find there are only two sets with the same sum. Mathematician No 2 is unable to choose between these until he also knows that there is an "Eldest" daughter.