I'm trying to prove that if $|G|=30=2\cdot 3\cdot 5$ then $G$ has a normal $3$-Sylow or a normal $5$-Sylow.
By the Sylow theorems, we would argue by contradiction in order to prove it cannot be $n_3=10$ and $n_5=6$ ($n_p$ is the number of $p$-Sylows).
In the second answer it is stated that if $n_3=10$ and $n_5=6$, then counting the number of distinct elements of these subgroups we have $10\cdot(3-1)+6\cdot(5-1)+1>30$.
However, I don't understand why this number is $10\cdot(3-1)+6\cdot(5-1)+1$. For example, is he saying that the number of elements of the $3$-Sylows (without the identity) is $10\cdot (3-1)$? Can anyone explain why? Wouldn't it be true only if they're disjoint?