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. 63
• B. 84
• C. 36
• D. 48

Answer 1

The correct option is D 48

Let $x$ be units digit and $y$ be tens digit, then number will be $10y+x$
Then,
$$x=2y$$
If 36 be added to the number, the digits are reversed, i.e number will be $10x+y$.
$$\begin{array}{cc}10y+x+36& =10x+y\\ 9x-9y& =36\\ x-y& =4\end{array}$$
Solving (1) and (2) we have $x=8$ and $y=4$.
Thus number is 48 .
Thus (c) is correct option.