Sudha is 34 years old today and her younger brother is 22. What was Sudha's age when her brother was half as old as he is now?

Half of the brother's present age is 11, and he was 11 exactly 22 - 11 = 11 years ago. Sudha was 11 years younger then, so she was 34 - 11 = 23. 17 halves Sudha's age as well, but only the brother's age was halved; both of them travel back by the same 11 years, not by the same fraction. 11 is the brother's age at that moment, the right date but the wrong person. 12 is the 12-year gap between them, which stays the same at every date and so can never answer a 'how old was she' question on its own.