Mr. Tik and Mr. Tak sold alarm clocks in the stores Before the Corner and Behind the Corner. Mr. Tik claimed that Before the Corner sold 30 more alarm clocks than Behind the Corner, while Mr. Tak claimed that Before the Corner sold three times as many alarm clocks as Behind the Corner. In the end, it turned out that both Tik and Tak were right. How many alarm clocks did they sell in both stores in total?

(L. Hozová)
From this information, it follows that if the number of alarm clocks sold in the store Behind the Corner represents one part, then the number of alarm clocks sold in the store In Front of the Corner represents three of these parts. From Tik's information, it then follows that two of these parts correspond to 30 alarm clocks. The total number of alarm clocks sold in both stores corresponds to four parts, so in total they sold $30+30=60$ alarm clocks.

Note. One part corresponds to 15 alarm clocks $(30: 2=15)$, so 15 alarm clocks were sold in the store Behind the Corner. In the store In Front of the Corner, they sold 45 alarm clocks, because $3 \cdot 15=45$. In both stores, they sold a total of $15+45=60$ alarm clocks.