If the average score is 90, the last digit is 0, that is, "the first digit +6+8 is a multiple of 9", because 6+8+0= 14, 14 = 18, and 18 can be divisible by 9, so it can only be 4.

Analysis shows that the number is 4680.

4680÷90=52 (person).

Law of division:

"Direct division" generally includes two forms in terms of questions:

First, when comparing multiple scores, the first larger/smaller number is larger/smaller in the case of equal size.

Second, when calculating the score, you can choose the correct answer by calculating the first place under different options.

"Direct score" is generally divided into three gradients according to the difficulty:

First, you can simply and directly see the first place to operate.

Second, you can see the first place of quotient through hands-on calculation.

Third, for some complicated scores, the first place of the "reciprocal" of the score needs to be calculated to determine the answer.