F.4 Maths

Let x be the tens digit.
Then the unit digit is x+5 and the two-digit number is 10x + (x + 5) = 11x + 5

From the condition given by the question,
(11x + 5) (x + x + 5) = 243
(11x + 5) (2x + 5) = 243
22x² + 65x + 25 = 243
22x² + 65x - 218 = 0
(22x + 109) (x - 2) = 0
x = -109/22 (Rejected) or x = 2

So the tens digit is 2 and the unit digit is 2+5 = 7
So the two-digit number is 27.


Hope it helps! ^^