Tính nhẩm:
a) 125 ⋅ 101. (Hướng dẫn: viết 101 = 100 + 1)
125 ⋅ 101 = 125 ⋅ (100 + 1)
=
= .
b) 21 ⋅ 49. (Hướng dẫn: viết 49 = 50 − 1)
21 ⋅ 49 = 21 ⋅ (50 − 1)
=
= .
12 625 125 ⋅ 100 + 125 ⋅ 1 1 029 125 ⋅ 100 − 125 ⋅ 121 ⋅ 50 + 21 ⋅ 121 ⋅ 50 − 21 ⋅ 1 12 3751 071 (Kéo thả hoặc click vào để điền)