Some cats got together and decided to kill mice numbering 999919.Each cat kills equal no.of mice and each cat kills more no.of mice than there were cats.Then what is the number of cats?
Laurent gives the accurate answer. As an extra explanation we can say :
where n is number of cats, and b is the difference between number of mice caught by cats and number of cats.
As Laurent said :
(991)(991 + b ) = 999919
b = 18
(991)(991 + 18 ) 999919