The average of the two-digit numbers, which remain the same when the dibits inter-change their positions, is :
Solution
Correct Answer: Option C
Average = (11 + 22 + 33 + 44 + 55 + 66 + 77 + 88 + 99) / 9
=( (11 + 99) + (22 + 88) + (33 + 77) + (44 + 66) + 55) / 9
= (4 \(\times\) 110 + 55)/9
= 495 / 9
= 55.
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