There are 20 red balls, 20 blue balls, 10 green balls, and 25 yellow balls. Her first selection is red and her second selection is green,
what is the probability that her third selection is blue given that she did not replace
the first two balls? Answer as a fraction in simplest form.

think about it deeply and passionately about this property

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graphically?   well, you graph them both, the solutions is where they both intersect each other, since there are two solutions, meaning they will meet twice, or namely the linear will run into the quadratic curve twice, and where they meet, those x,y coordinates are the solutions to the system.