When Teddy was $$5$$ years old, his father\textquotesingle s age was $$7$$ times his age. When his father is $$42$$ years old, how old will Teddy be? 
Overseas Competition->Knowledge Point->Word Problem Modules->Age Problems->When..., When... Type Age Problems
$$7\times5=35$$,  His father was $$35$$ years old when Teddy was $$5$$ years old.  Age difference $=35-5=30$  $42-30=12$ years old  $\textasciitilde$  or  $\textasciitilde$  $$7\times5=35$$,  His father was $$35$$ years old when Teddy was $$5$$ years old.  $$42-35=7$$ years later  $$5+7=12$$ years old  $\textasciitilde$  Teddy will be $$12$$ years old when his father is $$42$$ years old. 