Question

In a number of two digits, unit's digit is twice the tens digit. If $36$ be added to the number, the digits are reversed. The number is

• A. $36$
• B. $63$
• C. $48$
• D. $84$

Answer 1

Answer: (C)

$48$

Let the tens digit be $x$.
Hence, the units digit will be $2x$
Number $=10\times \left(x\right)+\left(2x\right)=12x$
When 36 is added to the number, the new number formed $=12x+36$
As the digits are reversed, we can also write the new number as $10\times \left(2x\right)+x=21x$
Hence,
$12x+36=10\times \left(2x\right)+x$
$\Rightarrow 12x+36=21x$
$\Rightarrow 21x-12x=36$
$\Rightarrow 9x=36$
$\Rightarrow x=4$
Hence, the original number $=12x=12\times 4=48$