BÀI 1:TÍNH NHANH
a, 128-28.(4-12)
b, (-28).32+58.(-28)+(-28).10
c,(-5-7):(-7+5)
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`a,`
`31/23-(7/32+8/23)`
`=31/23-7/32-8/23`
`=(31/23-8/23)-7/32`
`=1-7/32=25/32`
`b,`
`38/45-(8/45-17/51-3/11)`
`=38/45-8/45+17/51+3/11`
`= (38/45-8/45)+17/51+3/11`
`=2/3+17/51+3/11`
`=1+3/11=14/11`
`c,`
`(1/3+12/67+13/41)-(79/67-28/41)`
`= 1/3+12/67+13/41-79/67+28/41`
`= 1/3+(12/67-79/67)+(13/41+28/41)`
`= 1/3+(-1)+1=1/3+(-1+1)=1/3+0=1/3`
`d,`
`1/5+(-1/6)+1/7+(-1/8)+1/9+1/8+(-1/7)+1/6+(-1/5)`
`= (1/5+ -1/5)+(-1/6+1/6)+(1/7+ -1/7)+(-1/8 +1/8)+1/9`
`= 0+0+0+0+1/9=1/9 .`
45-58+(-45)+(+58)-3=45-58-45+58-3=(45-45)+(58-58)-3=-3
(-57)-(-12)+3-(-57)=-57+12+3+57=(-57+57)+12+3=15
-(-24)-(-30)+(-24)-30+8=24+30-24-30+8=(24-24)+(30-30)+8=8
-(-12)+(+19)-(+12)+8-19=12+19-12+8-19=(12-12)+(19-19)+8=8
47-(-53)+(-47)-(+53)=47+53-47-53=(47-47)+(53-53)=0
-(+28)+32-(-28)+(-34)=-28+32+28-34=(-28+28)-(34-32)=-2
15-(+72)+(-15)+(+72)=15-72-15+72=(15-15)+(72-72)=0
20-(+46)+(-25)-(-46)=20-46-25+46=(20-25)+(46-46)=-5
28-(-32)+(-28)-32+5=28+32-28-32+5=(28-28)+(32-32)+5=5
-75+(-49)+(+75)+49-12=-75-49+75+49-12=(-75+75)+(49-49)-12=-12
\(...=45-58-45+58-3=-3\)
\(...=-57+12+3+57=15\)
\(...=24+30-24-30+8=8\)
\(...=12+19-12+8-19=8\)
\(...=47+53-47-53=0\)
\(...=-28+32+28-34=-2\)
\(...=15-72-15+72=0\)
\(...=20-46-25+46=-5\)
\(=...28+32-28-32+5=5\)
\(...=-75-49+75+49-12=-12\)
a) = 1/2 - 1/2 + 1/3 -1/3 + 1/4 - 1/4 + 1/5 - 1/5 + 1/6
= 0 + 0 + 0 + 0 + 1/6
= 1/6
b) 2/3 + 2/4 - 2/4 + 2/5 - 2/5 + 2/6 - 2/6 + 2/7 - 2/7 + 28
= 2/3 + 28
= 86/3
[tick cho mik nha]
a)
\(\left(-11\right).\left(-28\right)+\left(-9\right).13\)
\(=308+\left(-9\right).13\)
\(=308+\left(-117\right)\)
\(=191\)
b)
\(\left(-69\right).\left(-31\right)-\left(-15\right).12\)
\(=\left(-69\right).\left(-31\right)+15.12\)
\(=2139+15.12\)
\(=2139+180\)
\(=2319\)
c)
\(\left[16-\left(-5\right)\right].\left(-7\right)\)
\(=\left[16+5\right].\left(-7\right)\)
\(=21.\left(-7\right)\)
\(=-147\)
d)
\(\left[\left(-4\right).\left(-9\right)-6\right].\left[\left(-12\right)-\left(-7\right)\right]\)
\(=\left[\left(-4\right).\left(-9\right)-6\right].\left[\left(-12\right)+7\right]\)
\(=\left[36-6\right].\left[\left(-12\right)+7\right]\)
\(=30.\left[\left(-12\right)+7\right]\)
\(=30.\left(-5\right)\)
\(=-150\)
b, 3/5 + 4/7 + 2/8 + 10/25 + 9/21 + 28/16
= 3/5 + 4/7 + 2/8 + 2/5 + 3/7 + 14/8
= (3/5 + 2/5) + ( 4/7 + 3/7) + ( 2/8 + 14/8)
= 1 + 1 + 7/4
= 2 + 7/4 = 15/4
c , 8/7 + 7/6 + 5/8 + 10/12 + 24/28 + 6/16
= c , 8/7 + 7/6 + 5/8 + 5/6 + 6/7 + 1/2
= (8/7 + 6/7) + (7/6 + 5/6) + 5/8 + 1/2
= 14/7 + 12/6 + 5/8 + 1/2
= 2 + 2 + 5/8 + 1/2
= 4 + 9/8 = 41/8
Bài làm
a) \(\left(\frac{3}{8}+\frac{-1}{4}+\frac{5}{12}\right):\frac{2}{3}\)
\(=\left(\frac{9}{24}+\frac{-6}{24}+\frac{10}{24}\right).\frac{3}{2}\)
\(=\frac{13}{24}.\frac{3}{2}\)
\(=\frac{39}{48}\)
b) \(\frac{-5}{7}.\frac{2}{11}+\frac{-5}{7}.\frac{9}{11}+1\frac{5}{7}\)
\(=-\frac{5}{7}.\left(\frac{2}{11}+\frac{9}{11}\right)+\frac{12}{7}\)
\(=-\frac{5}{7}.1+\frac{12}{7}\)
\(=\frac{7}{7}\)
\(=1\)
c) \(0,25:\left(10,3-9,8\right)-\frac{3}{4}\)
\(=\frac{25}{100}:\left(0,5\right)-\frac{3}{4}\)
\(=\frac{5}{4}:\frac{1}{2}-\frac{3}{4}\)
\(=\frac{5}{4}.2-\frac{3}{4}\)
\(=\frac{5}{2}-\frac{3}{4}\)
\(=\frac{10}{4}-\frac{3}{4}=\frac{7}{4}\)
d) \(-\frac{5}{9}.\frac{13}{28}-\frac{13}{28}.\frac{4}{9}\)
\(=-\frac{13}{28}\left(\frac{5}{9}+\frac{4}{9}\right)\)
\(=-\frac{13}{28}.\frac{9}{9}\)
\(=-\frac{13}{28}.1\)
\(=-\frac{13}{28}\)
a, 128 - 28.(4 - 12)
= 128 - 28.(-8)
= -8 . (-16) - 28 . (-8)
= -8 . (-16 - 28)
= -8 . (-44)
= 352
b, (-28) .32 + 58.(-28) + (-28) . 10
= -28 . (32 + 58 + 10)
= -28 . 100
= -2800
c, (-5 - 7) : (-7 + 5)
= -12 : (-2)
= 6