Tính nhẩm :

$1 \times 2 = ....$          $1 \times 3 = ....$

$2 \times 1 = ....$          $3 \times 1 = ....$

$2:1 = ....$            $3:1 = ....$

$1 \times 4 = ....$          $1 \times 5 = .....$

$4 \times 1 = ....$          $5 \times 1 = ....$ 

$4:1 = .....$          $5:1 = .....$

$1 \times 1 = .....$  

$1:1 = .....$

Số ?

Tính

a)

$\eqalign{   2 \times 3 \times 1 &= ......  \cr  & {\rm{             = }}...... \cr}$                        $\eqalign{   2 \times 1 \times 3 &= ......\cr  & {\rm{             = }}...... \cr}$

b)

$\eqalign{   4 \times 5:1 &= ...... \cr  & {\rm{             = }}...... \cr}$                        $\eqalign{   4:1 \times 5 &= ......  \cr  & {\rm{             = }}...... \cr}$

c)

$\eqalign{   8:4 \times 1 &= ......  \cr  & {\rm{             = }}...... \cr}$                        $\eqalign{   8 \times 1:4 &= ......  \cr  & {\rm{             = }}...... \cr}$

d)

$\eqalign{   12:3:1 &= ......  \cr  & {\rm{             = }}...... \cr}$                        $\eqalign{   12:1:3 &= ......  \cr  & {\rm{             = }}...... \cr}$

Điền dấu $\times$ hoặc $:$ thích hợp vào ô trống.