Permutations!!!

Find the number of 2-subsets of the set {1,2,.....10} , sum of whose elements is divisible by 3.

3 Answers

62
Lokesh Verma ·

Someone called nishant went mad yet again :)

341
Hari Shankar ·

sir, lagta hey thodi si galti ho gayi hey.

Total number of subsets is 10C2 = 45.

Number of subsets, where both are of the form 3k is 3C2 = 3

Where one is of the form 3k+1 and the other 3k-1 is 4X3 = 12

So the prob is 1/3

62
Lokesh Verma ·

oops :)

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