###
**A student finds the average of ten 2 digits numbers. While copying numbers, by mistake, he writes in number with its digits interchanged. As a result his answer is 1.8 less than the correct answer. The difference of digits of the number, in which he made mistake is ?**

A. 2
B. 3
C. 4
D. 6
**Answer: Option A**

## Show Answer

Solution(By Apex Team)

Let us consider by mistake he writes 10th number with its digits interchanged.
$\begin{array}{l}\therefore\frac{10x+y-(10y+x)}{10}=18\\
\end{array}$
(In this remaining nine numbers are same and they cancel out)
$\begin{array}{l}\text{∴ 10x + y – 10y – x = 18}\\
\text{⇒ 9x – 9y = 18}\\
\text{⇒ x – y = 2}\end{array}$

## Related Questions On Average

### Ajit has a certain average for 9 innings. In the tenth innings, he scores 100 runs thereby increasing his average19 people went to a hotel for combine dinner party 13 by 8 runs. His new average is:

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