At least one of x and y is 85. Suppose x is 85.

Again, the average score is 90 points.

∴110 (85+88+95+124+85+y+85+72+88+109) = 90, and the other number is 69?

∴ The poor performance of this 10 student is 124-69=55.

∴ 10 What is the variance of students' grades? = 1/ 10[? (85-90)? +(88-90)? +(95-90)+? ( 124-90)+(85-90)+(69-90)? +(85-90)+(72-90)+(88-90)? +? ( 109-90)]=239

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