39×21=819;
3 9
×
2 1
3 9
7 8 8 1 9
750÷5=150;
1 5 0
5
7 5 0
5 2 5
2 5 0
34×25=850;
3 4
×
2 5
1 7 0
6 8 8 5 0
791÷7=113;
1 1 3
7
7 9 1
7 9
7 2 1
2 1 0
验算:
1 1 3
×
7
7 9 1