(1)213×31=6603;
答:积是6603.
(2)130×42=5460;
(3)15×20+60,
=300+60,
=360;
答:这个数是360.
(4)99×15≈1500;
99×15,
=(100-1)×15,
=100×15-1×15,
=1500-15,
=1485;
1500-1485=15;
答:最大的两位数的15倍大约是1500,估算结果与乘得的准确数相差15.
(1)145×12=1740
答:145的12倍是1740.
(2)322×24=7728
答:积是7728.