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The number of seven digit integers, with sum of the digits equal to 10 and formed by using the digits 1, 2and 3 only, isA. 55B. 66C. 77D. 88

Answer» A seven digit number using 1, 2, and 3 and having 10 as the of digits can be formed either by using digits 1, 1, 1,1,1,2,3or,1,1,1,1,2,2,2.
So, required number of seven digit numbers
`=(7!)/(5!)+(7!)/(4!3!)=42+35=77`


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