There is overhead but Vulkan allows you to batch draw calls in a far more efficient manner. It can also generally use multi threading to feed a GPU even if the game isn’t coded with that in mind. Basically Vulkan offers so many improvements to efficiency and parallelization that the overhead is a drop in the bucket compared to the overall speedup in draw call optimization alone.

It has nothing to do with the answer being wrong, it’s how you get there. If you fail to subtract seven, realize your mistake, and correct it you have already passed the test. People with dementia will either start to count down by the wrong amount, start counting up, stuff like that. You are testing whether they can abstract verbal instructions and maintain a consistent train of thought while performing trivial calculations.

Counting down on your fingers one by one and only saying every seventh number would be considered a perfect score once you make it to about 63 if you don’t lose track of what you are doing or start forgetting numbers.