OK, the owners manual says we have a 10 quart transmission capacity, when we drain it, (quick drain, pull the pan plug, wait ten minutes) we get about four quarts, refill it with four quarts, it's now 40% changed and 60% contaminated.
Run it a day, and again drain four quarts. Now what do we have? We have again changed 40% of a 60% contaminated mixture.
Which gives us 36% still contaminated and 64% fresh.
A third change gives 21.6% contaminated, and 78.4 clean.
Do it again, and after the fourth change, you get 12.96% contaminated and 87.04% clean. After the fifth change, you get 7.776% contaminated and 92.224% clean.
So, after SIX changes, you have 4.6656% contaminated and 95.3344% clean and shiny new oil
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Math provided by Diana
(Edited by Di, too. Sorry, I missed a step in my calcs.
It's right, now.
)