Let's assume Sarah picked a total of x apples.
Sarah discarded 1/10 of the apples, so the number of apples remaining is x - 1/10 * x = 9/10 * x.
Out of these remaining apples, 300 were made into cider, so the number of apples sold as fresh fruit is 9/10 * x - 300.
Therefore, the fraction of the total apples picked that were sold as fresh fruit is:
(9/10 * x - 300) / x
Simplifying this fraction, we get:
(9x - 3000) / 10x