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4.Average
medium
The average of the two-digit numbers, which remain the same when the digits interchange their position is
A
$33$
B
$44$
C
$55$
D
$66$
Solution
Such two digit numbers are $11,22,33,44,55,66,77,88$ and $99 .$
Sum of these number $=11(1+2+3+…..+9)$
$=11 \times \frac{9}{2}(1+9)=11 \times \frac{9}{2} \times 10=495$
Average $=\frac{495}{9}=55$
Standard 13
Quantitative Aptitude
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