A7. What is the smallest positive difference between two fractions with both the numerator and the denominator being a positive integer less than or equal to 10?
(A) $\frac{1}{100}$
(B) $\frac{1}{99}$
(C) $\frac{1}{90}$
(D) $\frac{1}{70}$
(E) $\frac{1}{10}$
A7. To make the difference of two fractions - written as a fraction again - as small as possible, the denominator must be as large as possible and the numerator as small as possible. The denominator can be a maximum of 90, the denominator of one fraction is then 10 and the other denominator is 9. The numerator is at least 1.

These values are assumed at $\frac{1}{9}-\frac{1}{10}$ and at $\frac{9}{10}-\frac{8}{9}$.