7,8 Authors: Spivak A.V., Yanenko I.V.

Nataша and Inna bought identical boxes of tea bags. It is known that one tea bag is enough for two or three cups of tea. This box lasted Nataша for 41 cups of tea, and Inna for 58. How many tea bags were in the box?
Note that there could not have been fewer than 20 tea bags in the box: if there were at least 19, then Inna would not have been able to drink more than $19 \cdot 3=57$ cups, but she drank 58. On the other hand, there could not have been more than 20 tea bags: if there were at least 21, then Natasha could not have drunk fewer than $21 \cdot 2=42$ cups, but she drank 41. Thus, there were 20 tea bags in the box: Inna brewed 18 tea bags three times and two tea bags twice, while Natasha brewed one tea bag three times and 19 tea bags twice.

## Answer

20 tea bags.