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The average of the two-digit numbers, which remain the same when the digits interchange their positions, is :

Answer:

Explanation:

Average = $\frac{11+22+33+44+55+66+77+88+99}{9}$
$=\frac{(11+99)+(22+88)+(33+77)+(44+66)+55}{9}$
$=\frac{4\times110+55}{9}=\frac{495}{9}=55$