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The number of seven digit integers, with...

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

A

55

B

66

C

77

D

88

Text Solution

Verified by Experts

The correct Answer is:
C
There are two possible cases
Case I Five 1's, one 2's, one 3's
Number of numbers `= (7!)/(5!) = 42`
Case II Four 1's three 2's
Number of numbers `= (7!)/(4!3!) = 35`
`therefore` Total number of numbers = 42 + 35 = 77
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