Question:
The difference of two-digit number and the number obtained by reversing its digits is always divisible by ———-.
Solution:
9
Let ab be any two-digit number, then we have
ab – ba = (10a + b)- (10b + a)
= 9a – 9b = 9(a – b)
Hence, ab – ba is always divisible by 9 and (a – b).