số

Số con cừu	1	2	5	8
Số chân cừu	4	8	…	…

Quan sát ví dụ trong sách giáo khoa rồi giải bằng 2 cách.

A)

Cách 1: 3 × 2 × 2                                                     cách 2: 3 × 2 ×2

= (3 × 2) × 2                                                            = 3 × ( 2 × 2)

= 6 × 2                                                                     = 3 × 4

= 12                                                                         = 12

B)

Cách 1: 5 × 2 × 4                                                     cách 2: 5 × 2 × 4

= (5 × 2) × 4                                                            = 5 × (2 × 4)

= 10 × 4                                                                   = 5 × 8

= 40                                                                         = 40