KVPY2012MathematicsSets and Relations
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 ?
Options
- A10
- B13
- C17
- D20
Correct answer
C. 17
Step-by-step solution
A = 1,2,6,7,11,12,16,17,21,22,26,27,31,32,36,37 & One of the element which is multiple of 5 B = 3,4,8,9,13,14,18,19,23,24,28,29,33,34,38,39 & One of the element which is multiple of 5