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

Step-by-step solution

There are two possible cases arise: 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 Total number of numbers =42+35=77