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
← IIT-JEE 2009 · Paper 1
MathematicsSingle correct+3 / -1Question 28 of 60
IIT-JEE 2009 · Paper 1, Mathematics question 28
Answer and worked solution
Official answer: C
Excess over all ones. Seven digits each at least 1 sum to 7, so the extra 3 must be shared out, with no digit getting more than 2 extra.
- One digit 3 (extra 2) and one digit 2 (extra 1): .
- Three digits equal to 2: .
Total .
(C)