# CAT 2015 | Question: 99

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Amol was asked to calculate the arithmetic mean of $10$ positive integers, each of which had $2$ digits. By mistake, he interchanged the $2$ digits, say $a$ and $b$, in one of these $10$ integers. As a result, his answer for the arithmetic mean was $1.8$ more than what is should have been. Then $b – a$ equals  ________

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