1. Long ago, nine identical books cost 11 rubles and some kopecks, while thirteen such books cost 15 rubles and some kopecks. How much did one book cost?
From the first condition, it follows that one book costs more than 122 kopecks, otherwise 122⋅9=1098 kopecks. Thus, the price of one book is 123 kopecks.
Official solution
Answer: 123 kopecks.
Criteria: correct answer without explanation - 2 points.
Source: NuminaMath-1.5,
licensed Apache-2.0.
Statement and solution reproduced as published; topic, difficulty and ordering added
by this site.