This is not the average of 3, so there is no way to get the average score. You can get an average score of 69 books, and the rest depends on the performance of each class. Give it to whoever behaves well. Each type (13 copies) is 80÷6= 13 (copies) ... 2 (copies).

Average is especially commonly used in mathematics. Calculate the average value of; Reconciliation and leveling; Apportionment; Distribute (profits, etc.). ) in proportion (or even).

Law of division:

The purpose of division is to find the quotient, but when you suddenly can't see how many quotients are contained in the dividend, you can try to estimate the quotient, see how many divisors are contained in the highest digit of the multiplicand (that is, how many times the quotient is contained), and then add several times the complement from the standard number to get the quotient.

Small array: When the dividend contains divisor 1, 2, 3 times, the period method is:

Dividend includes quotient 1 multiple: the complement is added once from the standard.

Dividends include two quotients: from standard to supplementary.

Dividends include three quotients: from standard to supplementary three times.