[ Inequalities Problems. Case Analysis]

Long, long ago, nine identical books cost 11 rubles and some kopecks, and thirteen such books cost 15 rubles and some kopecks.

How much did one book cost

#
From the first condition, it follows that one book cost more than ${ }^{11} / 9=1.222 \ldots$ rubles, and from the second - that it cost less than ${ }^{16} / 15=1.2307 \ldots$ rubles.

## Answer

1 rub. 23 kop.