In a two digit positive number, the digit in the units place is equal to the square of the digit in ten's place, and the difference between the number and the number obtained by interchanging the digits is 54. What is 40% of the original number?
15.6
39
37.2
24
Solution
Let the number is $\Rightarrow 10x + y$
Now according to the question
$(10y + x) - (10x + y) = 54$ ... (i)
and $y = x^2 $ .... (ii)
$\Rightarrow$ Putting the value of (ii) in (i)
$\Rightarrow~10x^2 + x - 10x - x^2 = 54$
$\Rightarrow~x^2 - x = 6$
$\Rightarrow~x = 3$ and $y = 9$
Number = 39
40% of the number = 15.6