JEE Advanced 2009 Mathematics question

The number of seven digit integers, with sum of the digits equal to 10 and formed by using the digits 1, 2 and 3 only, is

Answer: (C)

Solution

Seven digits each at least 1 already sum to 7, so the extra 3 must be distributed by turning some 1s into 2s or 3s. Either one digit is 3 and

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Question ID VK-037698