Number System Practice Test 2

Let x be the digit in units place. Digit in ten’s place is then 15 - x.
∴ The number = 10 (15 – x) + x
The new number with reverse digits = 10 × x + (15 – x)
∴ 10(15 – x) + x + 9 = 10x + 15 – x
⇒ 150 – 10x + x + 9 = 9 x + 15
⇒ 18x = 144
$\Rightarrow \mathit{x}=\frac{144}{18}=8$
The digit of ten’s place = 15 – 8 = 7
∴ The required number = 78.