Question

Let $S=\{1,2,3,.....40\}$ and let $A$ be a subset of $S$ such that no two elements in $A$ have their sum divisible by $5$ What is the maximum number of elements possible in $A$?

• A. $10$
• B. $13$
• C. $17$
• D. $20$

Answer 1

The correct option is C $17$

There are $20$ maximum number of elements possible in $A$

$A=(1,2,5,6,7,11,12,15,16,17,21,22,25,26,27,31,32,35,36,37)$