A class mathematics test 60 to 70 points, 5 people 70 to 80 points, 8 people 80 to 90 points, 15 people 90 to 100 points, 12 people ask what percentage of the total number of students with 80 points or more? What percentage of the total number of students with 70 to 80 points or more?

5 + 8 + 15 + 12 = 40 (person)
（15+12）/40=67.5％
8 / (15 + 12) = 8 / 27

Xiao Ming looked at his score table and predicted: if the next math exam is 100 points, then the total average score is 91 points, if the next exam is 80 points, then the total average score of math is 86 points, Xiao Ming's math statistics table is already available______ This is a test

Let's have taken the test X times. According to the meaning of the test, the formula is: & nbsp; & nbsp; & nbsp; (x + 1) × 91-100 = (x + 1) × 86-80, & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; 91x + 91-100 = 86x + 86-80 & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp

10. Xiaoming looks at his math score table and predicts that if he gets 100 points in the next test, the total average score of math is 91 points; if he gets 80 points in the next test, the total average score of math is only 86 points. How many times has Xiaoming got in his math score table?

① If you're a junior high school student,
Suppose that there are x scores in Xiaoming's mathematical score table, and the total score of X scores is y, then
(100 + y) / (x + 1) = 91 and (80 + y) / (x + 1) = 86
Using these two equations, we can get x = 3, so we have got three results
② If you're a primary school student,
100-80 = 20, 91-86 = 5 the score difference between the two examinations is 20 points, and the average score difference is 5 points, so that 20 points should be averaged to four times, that is, 20 △ 5 = 4. This question is to ask you how many times you have already got the score, then not counting the score you will take this time, you have taken the examination three times before, that is, 4-1 = 3

Xiao Ming looked at his math score table and predicted that if he got 100 points in the next test, the total average score of math would be 91 points; if he got 80 points, the total average score of math would only be 91 points
So hard!

The question is, how many times is it this time? Otherwise, there will be no solution
If it's the first time, Xiaoming's math score this time is 2x91-100 = 82
If Xiaoming gets 80 points next time, the total average score of mathematics is only (80 + 82) / 2 = 81

A class mathematics test 60 to 70 points, 5 people 70 to 80 points, 8 people 80 to 90 points, 15 people 90 to 100 points, 12 people ask what percentage of the total number of students with 80 points or more? What percentage of the total number of students with 70 to 80 points or more?