Any math guru's out there? This is probably a very simple formula for you but I could use some verification of my math - or if I'm totally off on how I'm figuring it out. The long and short of it is that I'll be doing some partial drain and fills of my transmission fluids (let's not get into why or other suggestions about this part, just stick to the math for now.) So, I can replace/drain 5 quarts out of 12 total each drain. That's around 41.6% new fluids. My goal is to drain and fill as many times as necessary to have at least less than 10% of the old fluid. So, here is how I think the math works. So first time would be: 5/12 = 41.6% new, 58.4% old Second time would be: 58.4 * .416 = 24.29% old fluid left Third time would be: 24.29 * .416 = 14.19% old fluid left Fourth/last time would be: 14.19 * .416 = 8.29% So each time I drain my thinking is that I would take the percentage of old fluid remaining and multiply it by the percent I would be replacing. To get to my goal of less than 10% old fluid I would have to drain and fill 4 times. Is this math correct?