10 - 11 year olds

I arrived yesterday to an odd town. I had to stay at the house that was numbered 43. The instructions to find my house where the following:

The houses line the sides of a  great avenue having this avenue trees planted in the middle.

The way that they are numbered is simple: from 12 to 98 but no double digits can be found in a number.

Facing opposite each other, the  houses have the same numbers, but inverted in order. Per example, 12 is in front of 21.

How many houses are there in this avenue?