A student finds average of 10,2 digit numbers. If digits of one of number is interchanged, average i

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4.Average

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

A

$4$

B

$3$

C

$2$

D

$5$

Solution

Let Average $_{10}=y$

$\operatorname{Sum}_{10}=10 \times y$

It digits of $1$ number is interchanged, new average $=y+3.6$

$Sum _{10}$ after interchanging digits $=10 y+36$

$ab \rightarrow 2$ digit no\% whose digits have been interchanged

$9(b-a)=36$

$b-a=4$

Standard 13

Quantitative Aptitude

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