Question

If the digit $1$ is placed after a two digit number whose tens' digit is $l$, and units' digit is $u$, the new number is:

• A. $10l+u+1$
• B. $100l+10u+1$
• C. $1000l+10u+1$
• D. $l+u+1$

Answer 1

The correct option is B $100l+10u+1$

If any digit q is appended to any number x, it's value becomes 10x+q.

So at first we have a number with tens' digit l and unit's digit u.

The number is 10l+u.

After placing one more digit 1,

it becomes 10(10l+u)+1

That is, 100l+10u+1.