Question

Find the sum of all unit place digit of the numbers formed with the digits $3,4,5,6,7$ taken all at a time using each digit only once in each number.

• A. $6666600$
• B. $600$
• C. $800$
• D. None

Answer 1

The correct option is B $600$

Each digit until be at unit place in $4!$ numbers found by permutations of others $4$ digits.

$\therefore$ Required sum $=4!(3+4+5\times 6+7)$

$=4!\left(25\right)$

$=600$

$\therefore$ Option $B$ is correct