Answer :

Miss Ada Jorkins must have been twenty-four and her little brother Johnnie three years of age, with thirteen brothers and sisters between.
There was a trap for the solver in the words "seven times older than little Johnnie."
Of course, "seven times older" is equal to eight times as old.
It is surprising how many people hastily assume that it is the same as "seven times as old."
Some of the best writers have committed this blunder.
Probably many readers thought that the ages 24½ and 3½ were correct.

Math Genius