thực hiện phép tính bằng cách hợp lý nhất :
a) 64.52 +37.52-2.26
b ) 16,88+9,76+3,12
c) 19/11 + ( 8/13+ 3/110
d ) 1/2:1/4-1/6
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Bài 1:
\(a.8,32+14,76+5,24=8,32+\left(14,76+5,24\right)\)
\(=8,32+20=28,32\)
\(b,16,88+9,76+3,12=\left(16,88+3,12\right)+9,76\)
\(=20+9,76=29,76\)
\(c,\left(\dfrac{2}{5}+\dfrac{7}{9}\right)+\dfrac{3}{5}=\left(\dfrac{2}{5}+\dfrac{3}{5}\right)+\dfrac{7}{9}\)
\(=1+\dfrac{7}{9}=\dfrac{16}{9}\)
\(d,\dfrac{19}{11}+\left(\dfrac{8}{13}+\dfrac{3}{11}\right)\)
\(=\left(\dfrac{19}{11}+\dfrac{3}{11}\right)+\dfrac{8}{13}=\dfrac{22}{11}+\dfrac{8}{13}\)
\(=2+\dfrac{8}{13}=\dfrac{34}{13}\)
13 - 12 + 11 - 10 - 9 + 8 - 7 - 6 + 5 - 4 + 3 + 2 - 1
= ( 13 - 12 + 11 - 10 + 8 ) - ( 9 + 1 ) - ( 6 + 4) + ( 3 + 2 + 5 ) - 7
= 10 - 10 - 10 + 10 - 7
= ( 10 - 10 ) - ( 10 - 10 ) - 7
= 0 - 0 - 7
= - 7
9976+865)+135=976+(865+135)=976+1000=1976
891+(799+109)=(891+109)+799=1000+799=1799
(2/5+1/9)+3/5=(2/5+3/5)+1/9=1+1/9=9/9+1/9=10/9
19/11+(8/13+3/11)=(19/11+3/11)+8/13=22/11+8/13=22/11+8/13=2+8/13=26/13+8/13=34/13
16.88+9.76+3.12=(16.88+3.12)+9.76=20+9.76=29.76
72.68+17.16+82.64=72.68+(17.16+82.64)=72.68+100=172.68
\(a,16,88+9,76+3,12-5,13\)
\(=\left(16,88+3,12\right)+\left(9,76-5,13\right)\)
\(=20+4,63\)
\(=24,63\)
\(b,\frac{19}{11}+\frac{8}{13}+\frac{3}{11}\)
\(=\left(\frac{19}{11}+\frac{3}{11}\right)+\frac{8}{13}\)
\(=2+\frac{8}{13}\)
\(=\frac{34}{13}\)
\(c,\frac{1}{2}\div\frac{1}{4}-\frac{1}{6}\)
\(=2-\frac{1}{6}\)
\(=\frac{11}{6}\)
4:
a: =4/15-2,9+11/15=1-2,9=-1,9
b: \(=-36,75+3,7-63,25+6,3=10-100=-90\)
c: \(=6,5+3,5-\dfrac{10}{17}-\dfrac{7}{17}=10-1=9\)
d: \(=\dfrac{13}{25}\left(-39,1-60,9\right)=\dfrac{13}{25}\left(-100\right)=-52\)
e: =-5/12-7/12-3,7-6,3=-1-10=-11
f: =2,8(-6/13-7/13)-7,2=-2,8-7,2=-10
1b 4/11+5/11=9/11 ;2/3+4/5=10/15+12/15=22/15 ;5/7+9/14=10/14+9/14=19/14 ;2+5/8=2/2+5/8=8/8+5/8=13/8
a) (865+135)+976=1000+976=1976
(891+109)+799=1000+799=1799
(2/5+3/5)+7/9=1+7/9=16/9
`@` `\text {Ans}`
`\downarrow`
`a.`
`A=(1/2-7/13-1/3)+(-6/13+1/2+1 1/3)`
`= 1/2 - 7/13 - 1/3 - 6/13 + 1/2 + 1 1/3`
`= (1/2 + 1/2) + (-7/13 - 6/13) + (-1/3 + 1 1/3) `
`= 1 - 1 + 1`
`= 1`
`b.`
`B=0,75+2/5+(1/9-1 1/2+5/4)`
`= 3/4 + 2/5 + 1/9 - 3/2 + 5/4`
`= (3/4+5/4)+ 1/9 + 2/5 - 3/2`
`= 2 + 1/9 - 11/10`
`= 19/9 - 11/10`
`= 91/90`
`c.`
`(-5/9).3/11+(-13/18).3/11`
`= 3/11*[(-5/9) + (-13/18)]`
`= 3/11*(-23/18)`
`= -23/66`
`d.`
`(-2/3).3/11+(-16/9).3/11`
`= 3/11* [(-2/3) + (-16/9)]`
`= 3/11*(-22/9)`
`= -2/3`
`e.`
`(-1/4).(-2/13)-7/24.(-2/13)`
`= (-2/13)*(-1/4-7/24)`
`= (-2/13)*(-13/24)`
`= 1/12`
`f.`
`(-1/27).3/7+(5/9).(-3/7)`
`= 3/7*(-1/27 - 5/9)`
`= 3/7*(-16/27)`
`= -16/63`
`g.`
`(-1/5+3/7):2/11+(-4/5+4/7):2/11`
`=[(-1/5+3/7)+(-4/5+4/7)] \div 2/11`
`= (-1/5+3/7 - 4/5 + 4/7) \div 2/11`
`= [(-1/5-4/5)+(3/7+4/7)] \div 2/11`
`= (-1+1) \div 2/11`
`= 0 \div 2/11 = 0`
f: \(=\dfrac{7}{19}\left(\dfrac{8}{11}+\dfrac{3}{11}\right)-\dfrac{12}{19}=\dfrac{7}{19}-\dfrac{12}{19}=\dfrac{-5}{19}\)
i: \(=\left(\dfrac{9}{24}-\dfrac{18}{24}+\dfrac{14}{24}\right)\cdot\dfrac{6}{5}+\dfrac{1}{2}=\dfrac{5}{24}\cdot\dfrac{6}{5}+\dfrac{1}{2}\)
=1/4+1/2=3/4
` 7/19 . 8/11 + 3/11 . 7/19 + (-12)/19 `
`= 7/19 . ( 8/11 + 3/11 ) + (-12)/19 `
`= 7/19 . 11/11 + (-12)/19`
`= 7/19 . 1 + (-12)/19 `
`= 7/19 + (-12)/19 `
`= -5/19 `
`( 3/8 + (-3)/4 + 7/12 ) : 5/6 + 1/2`
`= 3/8 + (-3)4 + 7/12 . 6/5 + 1/2`
`= ( 9+(-18) + 14)/24 . 6/5 + 1/2`
`= 5/24 . 6/5 + 1/2`
`= 1/4 + 1/2 `
`= 3/4`