3. Phép nhân hai số tự nhiên. Dạng 2. Tính nhẩm

$46.99$$=46.\left(100-1\right)$$=46.100-46.1$$=4600-46$=4554

$47.98$$=47.\left(100-2\right)$$=47.100-47.2$$=4700-94$=4606

$18.19$$=18.\left(20-1\right)$$=18.20-18.1$$=360-18$=312

$24.198$$=\text{\hspace{0.17em}}24.\left(200-2\right)$$=24.200-24.2$$=4800-48$$=4752$

$1800.5$$=\left(1800:2\right).\left(5.2\right)$$=900.10$$=9000$

$36.25$$=\left(36:4\right).\left(25.4\right)$$=9.100$=900

$36600:50$$=\left(36600.2\right):\left(50.2\right)$$=73200:100$$=732$

$220000:\text{\hspace{0.17em}\hspace{0.17em}}5000$$=\left(220000.2\right):\left(5000.2\right)$$=440000:100$$=4400$