Being the one who does the arithmetic

You are the one in the house who knows what a number is a percentage of, and for the first time that has been named as a division of labour rather than a flaw in you.

It shows up in waiting rooms and car parks, where a bill lands and you have already worked out what share of something larger it is. What changed is that you said it out loud to Danny instead of keeping the sum private, and he answered that he already knew you did it and that it is not a bad thing to have one of you who does.