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4.Average
easy
A student finds the average of ten $2 -$digit numbers. While copying numbers, by mistake, he writes one number with its digits interchaged. As a result his answer is $1.8$ less than the correct answer. The diference of the digits of the number, in which he made mistake, is
A
$2$
B
$3$
C
$4$
D
$6$
Solution
Difference in average $=1.8$
Difference between the number and the number formed by inter changing the digits $=1.8 \times 10=18$
By Hit and Trial $\Rightarrow 53-35=18$
Number $=35 \Rightarrow$ Difference $=5-3=2$
Standard 13
Quantitative Aptitude