Question

The sum of the digits in the unit's place of all the 4-digit numbers formed by using the numbers 3, 4, 5 and 6, without repetition, is :

• A. $432$
• B. $108$
• C. $36$
• D. $18$

Answer 1

The correct option is B $108$

We have, $3,4,5,6$

$=3!(6+5+4+3)$

$=6\times 18$

$=108$