Question

If Alex finishes one chapter of a book on every ninth days. How many chapters will he finish in the next 30 days if he starts the first chapter today?

Answer 1

If Alex starts the first chapter today, he will finish it on the 9th day.
Then, he will take another 9 days to finish the second chapter on the 18th day.

Thus, the days on which he finishes the chapter are in multiples of 9.
Multiples of 9 till 30 are:
9 x 1 = 9
9 x 2 = 18
9 x 3 = 27

9 x 4 = 36, but this will be greater than 30.

Thus, Alex will be able to finish only three chapters in the next 30 days.