Question

Sorry if this question has been asked before but I couldn’t find a good match for what I am trying to do.

I am looking for an algorithm to do the below in C# (or relevant LINQ extensions).

Given a number within a set of numbers (e.g. 56 of 1 to 245) not excluding any numbers
and a partition size (e.g. 10)
I want to find the starting number for the partition that the given number is in.

Example:
Searching for the starting page of 56.

1-10
11-20
21-30
31-40
41-50 
51-60 <-- 56 is in the partition starting with 51
..
231-240
241-245

Answer 1

int page = 56;
int partition_size = 10;

int starting_number = (page / partition_size) * partition_size + 1;