Question

A certain number of two digits is four times the sum of the digits. If $9$ is added to the number, the digits in the number are reversed. Find the number.

• A. $13$
• B. $15$
• C. $12$
• D. $14$

Answer 1

The correct option is C $12$

Let the tenths digit be y and units digit be x.
The number will be $10y+x$
As per the problem, $10y+x=4(x+y)$ ............. (1)
$10x+y=(10y+x)4$ ........(2)
Solving (1) and (2), we get $x=2,y=1$.
Therefore, the number is 12.