Katherine earned 84, 92, 84, 75, and 70 on her five math tests.
What is the minimum grade Katherine needs to earn on the next test to have a mean of 84?

Katherine's marks = 84,92,84,75,70

Total marks = 84+92+84+75+70 = 405

No. of observations = 5

Mean = Total sum of observations/No. of observations

Mean = 405/5=81

Expected mean = 84

Let expected total marks be = n

84=n/5

84×5=n

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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.