1) Divide 13-9 by a previous continuous subtraction, divide 9 by 3 and 6, subtract 3 from 13, and then subtract 6 to get 13-9=4. The basis of this algorithm is that children have mastered the division and combination of numbers within 10, and can calculate the subtraction within 10, the subtraction of more than ten and the subtraction of more than ten.

(2) Think of 13 minus 9 as 13 minus 10 by "multi-minus plus complement method", and add 1, that is, 1 3-9 =.

(3) Use "want to add and subtract" to make use of the relationship between addition and subtraction. As long as we know how much 9 plus equals 13, we can deduce how much 13 minus 9 equals. The basis of this algorithm is that the child will write the corresponding subtraction formula according to the addition formula, find out the unknown in brackets and calculate the carry addition within 20. If carry addition is very skilled, this method will be calculated quickly, children's reverse thinking will be exercised, and the close relationship between addition and subtraction will be better understood.