A premise assumption is needed, that is, the problem must be discussed in an integer range, and each drop of ink only covers one number, otherwise the solution of the problem is definitely not unique. The title only said that the ink covered some numbers, but did not explain any information about the covered parts. Ink can be large or small, and it can even be understood as a decimal point cover. Therefore, the following discussion is based on the above two basic assumptions.

First of all, let's assume that the single digit of the math score is X and the average ten digits are Y.

The value range of x is 0, 1, 2, ..., 9.

The range of y is 1, 2, ..., 9.

According to the method of calculating the average score, the equation can be listed:

10y+5 =(79+85+8 1+90+90+x)/5

50y+25=425+x

50y=400+x

y=8+x/50

Since we assume that the problem is discussed in an integer range, X must be divisible by 50, and the value range of X is 0, 1, 2, ..., 9. So x=0, and then y=8.

So, math: 90, average score: 85.