Madhya Pradesh Police Exam Model Paper 5

Given:
The sum of the digits of a number is 18 less than the number
Concept used:
If the number is 'xy' It can also write $10\mathit{x}+\mathit{y}$
Where x is tenth place digit and y is unit place digit
Calculations:
Let the number be 'ab'
So, Number $=10\mathit{a}+\mathit{b}$
According to question
$\mathit{a}+\mathit{b}=10\mathit{a}+\mathit{b}\mathit{–}18$
$\Rightarrow 9\mathit{a}=18$
$\Rightarrow \mathit{a}=2$
∴ The digit in the tens place of the number is 2