Tính bằng hai cách theo mẫu:
Mẫu: 452 × 39 = 452 × (30 + 9)
= 452 × 30 + 452 × 9
= 13560 + 4068 = 17628
452 × 39 = 452 × (40 – 1 )
= 452 × 40 + 452 × 1
= 18080 - 452 = 17628
a) 896 × 23 = ………………
b) 547 × 38 = ………………
a) 896 × 23 = 896 × (20 + 3)
= 896 × 20 + 896 × 3
= 17920 + 2688
= 20608
896 × 23 = 896 × (24 – 1 )
= 896 × 24 – 896 × 1
= 211504 – 896
= 20608
b) 547 × 38 = 547 × (30 + 8)
= 547 × 30 + 547 × 8
= 20786
547 × 38 = 547 × (39 – 1)
= 547 × 39 - 547 × 1
= 21333 – 547
= 20786
-- Mod Toán lớp 4