08-11-2014, 11:54 PM
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
Solution
in this sum two cases arises they are
case - 1
7! / 5! = 7 * 6 = 42
case -2
7! / ( 3! * 4! ) = 35
hence the required no of 7 digit numbers is 42 + 35 = 77
so the choice c is correct answer
a. 55
b. 66
c. 77
d. 88
Solution
in this sum two cases arises they are
case - 1
7! / 5! = 7 * 6 = 42
case -2
7! / ( 3! * 4! ) = 35
hence the required no of 7 digit numbers is 42 + 35 = 77
so the choice c is correct answer