smc

Tom's age $N$ years ago was $T-N$. The sum of the ages of his three children $N$ years ago was $T-3N,$ since there are three children. If his age $N$ years ago was twice the sum of the children's ages then, $$\begin{array}{rl}T-N& =2(T-3N)\\ T-N& =2T-6N\\ T& =5N\\ T/N& =\boxed{5}\end{array}$$ Note that actual values were not found.