Let n be the number we are looking for.
It has, at least, two digits + a tens digit which can be represented as ab.c where a, b, and c is a number from 1 to 9.
The first part of the problem can be written mathematically as:
The second part of the sentence states that:
From the first equation, c could be equal to 1, 2, 3, 4, 5, or 6 since a+b cannot be greater than 18 nor lesser than 0 (that would imply a=b=c=0).