What is the value of old German money zehn millarden mark dated October 1 1923?

Answer 1

You have a bill from the period of hyperinflation that followed WW1.

Germany was ordered to pay reparations to the victorious Allies following the 1918 armistice. The amounts demanded were so large that the economy was ruined; the government responded by printing more and more currency resulting in inflation so fast that at its worst period prices would go up multiple times per DAY. The mark was frequently revalued in an effort to keep up, which is why your bill has a specific day printed on it.

I checked a German collector's site and found that the printed value is ten billion marks, which was worth all of one U.S. dollar at the time. The years have helped a bit; in average condition your bill would now retail for about $10 U.S.