Question:
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
Correct Option: , 3
Solution:
(I) First possiblity is $1,1,1,1,1,2,3$
required number $=\frac{7 !}{5 !}=7 \times 6=42$.
(II) Second possiblity is $1,1,1,1,2,2,2$
required number $=\frac{7 !}{4 ! 3 !}=\frac{7 \times 6 \times 5}{6}=35$
Total $=42+35=77$
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