A student finds the average of 10, 2 digits numbers. If the digits of one of the numbers interchanged, the average increases by 3.6. The difference between the digits of the 2 digits number is :

A. 4

B. 3

C. 2

D. 5

Answer: Option A

Solution(By Examveda Team)

According to the question,
Let as consider by mistake he writes 10th number with its digits interchanged
∴ $$\frac{{10x + y - \left( {10y + x} \right)}}{{10}} = 3.6$$
∴ In these remaining nine numbers are same and they cancel out
$$\eqalign{ & \Rightarrow \frac{{10x + y - \left( {10y + x} \right)}}{{10}} = 3.6 \cr & \Rightarrow 9x - 9y = 36 \cr & \Rightarrow x - y = 4 \cr} $$