Bài 7: Tính nhanh
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 –256.444
p) 43.37 + 93.43 + 57.61 + 69.57 q) 38. 63 + 37. 38
r) 35.34 +35.38 + 65.75 + 65.45
c, 3.25.8 + 4.37.6 + 2.38.12
= (3.8).25 + (4.6).37 + (2.12).38
= 24.25 + 24.37 + 24.38
= 24.(25 + 37 + 38)
= 24.100
= 2400
d, (1200 + 60):12
= 1200: 12 + 60: 12
= 100 + 5
= 105
e, 12.53 + 53.172 - 53.84
= 53.(12 + 172 - 84)
= 153.( 184 - 84)
= 153. 100
= 15300
g, (2100 - 42): 21
= 2100 : 21 - 42: 21
= 100 - 2
= 98
h, 39.8 + 60.2 + 21.8
= (39.8 + 21.8) + 60.2
= 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 + 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
= (37.7 + 43.7) + 80.3
= 7.(37 + 43) + 80.3
= 7.80 + 80. 3
= 80.(7 + 3)
= 80.10
= 800
m, 113.38 + 113.62 + 87.62 + 87.38
= (113.62 + 87.62) + (113.38 + 87.38)
= 62.(113 + 87) + 38.( 113 + 87)
= 62.120 + 38. 120
= 120.(62 + 38)
= 120.100
= 12000
n, 123.456 + 456.321 - 256.444
= (123.456 + 456.321) - 256.444
= 456.(123 + 321) - 256.444
= 456.444 - 256.444
= 444.( 456 - 256)
= 444. 200
= 88800
p, 43.37 + 93.43 + 57.61 + 69.57
= (43.37 + 93.43) + (57.61 + 69.57)
= 43.(37 + 93) + 57.(61 + 69)
= 43.100 + 57.100
= 100.(43 + 57)
= 100.100
= 10000
q, 38.63 + 37.38
= 38.(63 + 37)
= 38.100
= 3800
