Question

The sum of the value of the digits at the tens place of all the numbers formed with the help of $3,4,5,6$ taken all at a time is

• A. $1080$
• B. $4320$
• C. $360$
• D. $180$

Answer 1

The correct option is A $1080$

Total number of numbers formed with the digits $3,4,5,6$ is $4!$ $=$ $24$

If a digit is fixed in tens place, number of numbers formed will be $6$

i.e for every digit in tens place there will be $6$ numbers formed

Now, sum of the digits $=(6\times 3)+(6\times 4)+(6\times 5)+(6\times 6)$ $=108$.

Now its value in tens place $=108\times 10=1080$.