First slide
Permutations
Question

Let A be a set of n (3) distinct elements. The number of triplets (x, y, z) of the A elements in which at least two coordinates is equal to 

Moderate
Solution

Total number of triplets without restriction is n x n x n. The number of triplets with all different coordinates is  nP3. Therefore, the required number of triplets is ,n3nP3

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