GMAT Quantitative Reasoning Practice Test 2

Since John spent all of the $\mathrm{\$}135$ on the tickets, their prices must sum up to $\mathrm{\$}135$. The Minimum amount spent for the $\mathrm{\$}12$ tickets, is the smallest amount that is divisible by 12 , and still leaves an amount divisible by 5 . $\mathrm{\$}60$ is the smallest amount both divisible by 12 and leaving $\mathrm{\$}135-\mathrm{\$}60=\mathrm{\$}75$, which is divisible by $\mathrm{\$}5$.