Question

If the digit $1$ is placed after a two digit number whose ten's digit is $t$ and unit's digit is $u$, then the new number is:

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

Answer 1

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

Given, ten's place digit $=t$ and one's place digit $=u$
Two digit number $=10\times$ten's place digit+one's place digit
$=10t+u=tu$

If the digit 1 is placed after a two digit number, the new number is $tu1$,

which now becomes a three digit number.

The hundreds place digit $=t$, ten's place digit $=u$ and one's place digit $=1$

$\therefore$ Number $=100\times$hundred's place digit + $10\times$ten's place digit + one's place digit
$=100t+10u+1$

So, Option B is correct.