Let the tens digit of the number be
a and ones digit be
b.
Given:
ab = 12 ................(i) and,
(10a + b) - (10b + a) = 9
10a + b - 10b - a = 9
9a - 9b = 9
9(a-b) = 9
(a-b) = 1 .................(ii)
Factors of 12 = 1, 2, 3, 4, 6, 12.
and from equation (ii), (a – b) = 1
So, a = 4 & b = 3.
Required number = ab = 43.
