S = {1, 2, 3, 4, 5, 6, 9} 3n Type numbers 3, 6, 9 3n −1 Type numbers 2, 5 3n − 2 Type numbers 1, 4 Let NP= Number of Subset of S containing p element which are not divisible by 3. For P = 1 2C1+2C1=4 For P = 2 3C12C1+3C12C1+2C2+2C2=14 For P = 3