Question

A pen cost ₹11 and a notebook cost ₹13. Find the number of ways in which a person can spend exactly ₹ 1000 to buy pens and notebooks.

Answer 1

Let x be the number of pens and y be the number of note books.
You can get this answer by substituting any value in the place of x or y. But note the number substituted should satisfy the equation by getting a perfect output. If you find first two numbers then you can predict other numbers easily because the common difference will be equal.
let x pens and y notebooks
11x + 13y = 1000
y = 5, 16, 27, 38, 49, 60, 71

Hence maximum 7 ways