Question 522491
Assuming there are a total of 100 points, 100/12 = 8 1/3 points per answer.
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To score at  least 90, means 90 or more.
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x = number of correct answers
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100/12*x >= 90
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100x = 1080
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x = 10.8
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Assuming you can only get full credit for an answer or no credit, then your son must get at least 11 of the 12 questions right to have a score of 90% or higher.
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Done.