`@` `\text {Ans}`
`\downarrow`
`67.21 + 33.22`
`= 67.7.3 + 3.11.22`
`= 3.(67.7 + 22.11)`
`= 3.(469 + 242)`
`= 3. 711`
`= 2133`
67.21+33.22
=(66+1).21+33.(21+1)
=66.21+21+33.21+33
=2.33.21+33.21+21+33
=3.33.21+54
=3.3.11.21+54
=9.(10+1).21+54
=(90+9).21+54
=(100-1).21+54
=2100-21+54
=2133
Tính nhanh:
67 \(\times\) 21 + 33 \(\times\) 22
= 67 \(\times\) 21 + 33 \(\times\) (21 +1)
= 67 \(\times\) 21 + 33 \(\times\) 21 + 33
= 21 \(\times\) (67 + 33) + 33
= 21 \(\times\) 100 + 33
= 2133
Sửa đề: \(67\cdot21+33\cdot21\)
\(=21\cdot\left(67+33\right)\)
\(=21\cdot100\)
\(=2100\)
