Bài 7: Tính nhanh
a) 37. 38 + 62. 37 b) 28. 64 + 28. 36
c) 3. 25. 8 + 4. 37. 6 + 2. 38. 12 d) (1200 + 60) : 12
e) 12.53 + 53. 172 – 53. 84 g) (2100 – 42) : 21
h) 39.8 + 60.2 + 21.8 i) 36.28 + 36.82 + 64.69 + 64.41
k) 32. 47 + 32. 53 l) 37.7 + 80.3 +43.7
m) 113.38 + 113.62 + 87.62 + 87.38 n) 123.456 + 456.321 –256
a. 37. 38 + 62. 37
= 37 . (38 + 62)
= 37 . 100
= 3700
b. 28. 64 + 28. 36
= 28 . (64 + 36)
= 28 . 100
= 2800
c. 3. 25. 8 + 4. 37. 6 + 2. 38. 12
= 3 . 8 . 25 + 4 . 6 . 37 + 12 . 2 . 38
= 24 . 25 + 24 . 37 + 24 . 38
= 24 . (25 + 37 + 38)
= 24 . 100
= 2400
e. 12.53 + 53. 172 – 53. 84
= 53 . (12 + 172 - 84)
= 53. 100
= 5300
h. 39.8 + 60.2 + 21.8
= 8 . (39 + 21) + 60 . 2
= 8 . 60 + 60 . 2
= 60 . (8 + 2)
= 60 . 10
= 600
i. 36.28 + 36.82 + 64.69 + 64.41
= 36 . (28 + 82) + 64 . (69 + 41)
= 36 . 110 + 64 . 110
= 110 . (36 + 64)
= 110 . 100
= 11000
k. 32. 47 + 32. 53
= 32 . (47 + 53)
= 32 . 100
= 3200
l. 37.7 + 80.3 +43.7
= 7 . (37 + 43) + 240
= 7 . 80 + 240
= 560 + 240
= 800
m. 113.38 + 113.62 + 87.62 + 87.38
= 113 . (38 + 62) + 87 . (62 + 38)
= 113 . 100 + 87 . 100
= 100 . (113 + 87)
= 100 . 200
= 20000
bài n thé này mới đúng
n. 123.456 + 456.321 –256 . 444
= 456 . (123 + 321) - 256 . 444
= 456 . 444 - 256 . 444
= 444 . (456 - 256)
= 444 . 200
= 88800
