When do you Multiply the runtimes, and when do you Add them?

If your algorithm is "do this, then, when you're all done, do that," then you add the runtimes.

Add Runtimes when operations are sequential and independent.

If your algorithm is "do this for each time you do that," then you multiply the runtimes.

Multiply Runtimes when operations are nested, or one operation depends on the iteration of another.

Big O is your tool to know when your algorithm gets faster or slower;

Master it!