1.  The sum of the digits of a two-digit number is 1/5 of the difference between the number and the number obtained by interchanging the position of the digits. What is definitely the difference between the digits of that number ?
A. 5
B. 7
C. 9
D. Data inadequate
E. None of these

Answer: Option D

Explanation:

Let the ten's digit be x and unit's digit be y.
Then, x + y = 1/5 [(10x + y) - (10y + x)]
⇒ 5x + 5y = 9x - 9y
⇒ 4x = 14y.
Thus, the value of (x - y) cannot be determined from the given data.