GATE | GATE-CS-2015 (Set 3) | Question 15

The number of 4 digit numbers having their digits in non-decreasing order (from left to right) constructed by using the digits belonging to the set {1, 2, 3} is ____.
(A) 12
(B) 13
(C) 14
(D) 15


Answer: (D)

Explanation: {1, 1, 1, 1}
{1, 1, 1, 2}
{1, 1, 1, 3}
{1, 1, 2, 2}
{1, 1, 2, 3}
{1, 1, 3, 3}
{1, 2, 2, 2}
{1, 2, 2, 3}
{1, 2, 3, 3}
{1, 3, 3, 3}

{2, 2, 2, 2}
{2, 2, 2, 3}
{2, 2, 3, 3}
{2, 3, 3, 3}

{3, 3, 3, 3}




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