Question

The sum of all the four digit numbers which can be formed using the digits $6,7,8,9$(repetition is allowed).

• A. $2133120$
• B. $2133140$
• C. $2133150$
• D. $2133122$

Answer 1

Answer: (A)

$2133120$

No. of 4 digits number can be formed $=4^4=256$

we consider units place then sum of all numbers at unit place = $\frac{256}{4}(6+7+8+9)$

$=64\left(30\right)=1920$

$\therefore$ sum of all fair digits =

$\left(1920\right)(1+10+100+1000)$

$=\left(1920\right)\left(1111\right)$

$=2133120$