Analysis:

This is the topic of an examination cycle.

1+2+3 = 6,80 ÷ 6 =13 ... 21A white pearl is followed by a red one, so the 80th one is red.

Extended data

Integer division:

1, divided by high dividend;

2. How many digits is the divisor? Look at the first few digits of the divisor first. If the divisor is not enough, look at another one.

3, in addition to which one, which one must be written on the business;

4. The remainder of each division must be less than the divisor;

5. After finding the highest bit of the quotient, if there is not enough quotient 1 on the dividend, write 0 on it.

Text expression:

Appendix+Appendix = sum, one addend = sum-another addend.

Minus-Minus = Difference, Minus = Minus-Difference, Minus = Difference+Minus.

Factor × factor = product, one factor = product ÷ another factor.

Dividend = quotient, divisor = dividend = quotient, dividend = quotient × divisor. ?