Question

The sum of the digits of a two-digit number is 5. When the digits are reversed, the number increases by 27. Find the original number. The original number is

Answer 1

14

Explanation:

`a-\text{tens digit}\\b-\text{unity digit}\\10a+b-\text{number}\\10b+a-\text{number with reversed digits}\\a+b-\text{sum of digits}\\\\\bold{System\ of\ equations:}\\\\\left\{\begin{array}{ccc}a+b=5\\10b+a=10a+b+27&\text{subtract}\ 10a\ \text{and}\ b\ \text{from both sides}\end{array}\right\\\\\left\{\begin{array}{ccc}a+b=5\\9b-9a=27&\text{divide both sides by 9}\end{array}\right`

`\underline{+\left\{\begin{array}{ccc}a+b=5\\b-a=3\end{array}\right}\qquad\text{add both sides of the equations}\\.\qquad2b=8\qquad\text{divide both sides by 2}\\.\qquad \boxed{b=4}\\\\\text{Put the value of\ b}\ \text{to the first equation}\\\\a+4=5\qquad\text{subtract 4 from both sides}\\\boxed{a=1}`