Câu 2: Trang 68 sách giáo khoa (SGK) Toán tiếng Anh lớp 4a) Calculated by the most convenient...

a) Calculated by the most convenient way:
1st way:
134 x 4 x 5 = (134 x 4) x 5 = 536 x 5 = 2680
5 x 36 x 2 = (5 x 36) x 2 = 180 x 2 = 360
42 x 2 x 7 x 5 = (42 x 2) x (7 x 5) = 84 x 35 = 2940

2nd way:
134 x 4 x 5 = (4 x 5) x 134 = 20 x 134 = 2680
5 x 36 x 2 = (36 x 2) x 5 = 72 x 5 = 360
42 x 2 x 7 x 5 = (2 x 7) x (5 x 42) = 14 x 210 = 2940

b) Calculate:
137 x 3 + 137 x 97 = 137 x (3 + 97) = 137 x 100 = 13700
428 x 12 - 428 x 2 = 428 x (12 - 2) = 428 x 10 = 4280
94 x 12 + 94 x 88 = 94 x (12 + 88) = 94 x 100 = 9400
537 x 39 - 537 x 19 = 537 x (39 - 19) = 537 x 20 = 10740