Ha! Incorrigibly nerdy ex-algebra teacher here. This is one of those mixture problems.
How much 2% solution and how much 36% solution must Andrea combine to get 1 cup of 10% solution? The answer is about 3/4 cups 2% and 1/4 cup heavy cream (which is about 36% milkfat).
But I'm sure equal parts works fine. That's what I put in my coffee when we're out of half and half.