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 .
77
We have to form 7digit numbers, using the digits 1, 2 and 3 only, such that the sum of the digits in a number = 10 .
This can be done by taking 2,2,2,1,1,1,1,or by taking 2,3,1,1,1,1,1.
∴ Number of ways =7!3!4!+7!5!=77.