Let P be the set of seven digit numbers with sum of their digits equal to 11 . If the numbers in P are formed by using the digits 1,2 and 3 only, then the number of elements in the set P is :
- (A)158
- (B)173
- (C)164
- (D)161✓ Correct
Answer: (D)
Solution
Let a 7-digit number use ones, twos and threes, so
Subtracting, , giving three integer solutions:
: digits , arrangements .
: digits , arrangements .
: digits , arrangements .
Total: .
Subtracting, , giving three integer solutions:
: digits , arrangements .
: digits , arrangements .
: digits , arrangements .
Total: .
JEE Main · 2025 · 29 Jan 2025 · Shift 1 · Single correct option