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-7/23*75/97+75/97-11/23*75/97
=75/97*(-7/23+11/23)
=75/97*4/23
=300/2231
(3/8+ -1/4+5/12):2/3
=(9/24+ -6/24+10/24):2/3
=13/24/2/3
=13/16
ai h cho minh minh h lai cho
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A = 2/1*5 + 2/5*9 + ... + 2/101*105
= 1/2(4/1*5 + 4/5*9 + ... + 4/101*105)
= 1/2(1 - 1/5 + 1/5 - 1/9 + ... + 1/101 - 1/105)
= 1/2(1 - 1/105)
= 1/2 * 104/105 = 52/105
Sửa câu b. Phân số thứ 2 phải là 4/5*8
B = 4/2*5 + 4/5*8 + ... + 4/47*50
= 4/3(3/2*5 + 3/5*8 + ... + 3/47*50)
= 4/3(1/2 - 1/5 + 1/5 - 1/8 + ... + 1/47 - 1/50)
= 4/3(1/2 - 1/50)
= 4/3 * 24/50 = 16/25
![](https://rs.olm.vn/images/avt/0.png?1311)
\(a,573+67-\left(573-23\right)\\ =573+67-573+23\\=\left(573-573\right)+\left(67+23\right)\\ =0+90\\ =90\\ b,\left(-73\right)-\left[2^3.5-6\right].2\\ =\left(-73\right)-\left[8.5-6\right].2\\ =\left(-73\right)-\left[40-6\right].2\\ =\left(-73\right)-34.2\\ =\left(-73\right)-68\\ =-141\)
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Bài 2. Tính nhanh
a) 27 + (-2019) + (-27)
= 27 -2019 -27
=(27 - 27) -2019
=0-2019
= -2019
d) (-102) – (345 – 102)
= -102 - 345 +102
= (102 - 102) -345
= 0-345
= -345
b) (-10) + 23 + (-20) + 30
= -10 +23-20+30
= -(10+20) +23 +30
= -30 +23 +30
= (30-30) +23
= 0 +23
= 23
e) (12 + 34 – 56) – (12 – 56)
= 12 +34 -56 -12 +56
= (12-12) + (56-56) +34
= 0+0 +34
= 34
c) (-2).125.(-5).(-8).(+17)
=[(-2) . (-5)] . [ 125.(-8)] . (+17)
= 10 . (-1000).(+17)
= - 10000 . 17
= - 170000
f) 37.(-345) – 345.(-47)
= -345 . (37-47)
= -345.(-10)
=3450
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`#3107.101107`
\(\left[2^3\cdot97+8\cdot75-\left(-47\right)\cdot2^3\right]\div10^2\)
\(=\left(2^3\cdot97+2^3\cdot75+47\cdot2^3\right)\div10^2\)
\(=\left[2^3\cdot\left(97+75-47\right)\right]\div10^2\)
\(=\left(2^3\cdot125\right)\div10^2\)
\(=\left(2^3\cdot5^3\right)\div10^2\)
\(=\left(5\cdot2\right)^3\div10^2\)
\(=10^3\div10^2\)
\(=10\)
\(\left(2^3.97+8.75-47.2^3\right):10^2\\ =\left[\left(97-47+75\right).2^3\right]:100\\ =\left[125.8\right]:100\\ =1000:100=10\)