a: =1/4-1/12=3/12-1/12=1/6
b: =3/8-3/4+1/2
=3/8-6/8+4/8=1/8
c: =-2/3+3/4-1/3
=-1+3/4=-1/4
d: =27/23-4/23+5/21+16/21+1/2
=2+1/2
=5/2
`1/4 - (1/6 - 1/12)`
`=1/4 - 1/6 + 1/12`
`=3/12 - 2/12 + 1/12`
`=(3-2+1)/12`
`=2/12`
`=1/6`
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`3/8 - (3/4-1/2)`
`=3/8-3/4+1/2`
`=3/8-6/8+4/8`
`=(3 - 6 + 4)/8`
`=1/8`
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`(-2/3) + 3/4 - (1/2 - 1/6)`
`=-2/3 +3/4 - 1/2 + 1/6`
`=-8/12 + 9/12 - 6/12 + 2/12`
`=(-8+9-6+2)/12`
`=-3/12`
`=-1/4`
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`27/23 -(-5/21)-4/23 + 16/21 + 1/2`
`=27/23 + 5/21 - 4/23 + 16/21 + 1/2`
`=(27/23 - 4/23) + (5/21 + 16/21) + 1/2`
`=23/23 + 21/21 + 1/2`
`=1+1+1/2`
`=2 + 1/2`
`=4/2 + 1/2`
`=5/2`
\(a,=\dfrac{1}{4}-\left(\dfrac{2-1}{12}\right)=\dfrac{1}{4}-\dfrac{1}{12}=\dfrac{3-1}{12}=\dfrac{1}{6}\\ b,=\dfrac{3}{8}-\left(\dfrac{3-2}{4}\right)=\dfrac{3}{8}-\dfrac{1}{4}=\dfrac{3-2}{8}=\dfrac{1}{8}\\ c,=-\dfrac{2}{3}+\dfrac{3}{4}-\left(\dfrac{3-1}{6}\right)=\dfrac{-2}{3}+\dfrac{3}{4}-\dfrac{1}{3}=-1+\dfrac{3}{4}=\dfrac{-4+3}{4}=-\dfrac{1}{4}\\ d,=\left(\dfrac{27}{23}-\dfrac{4}{23}\right)+\left(\dfrac{5}{21}+\dfrac{16}{21}\right)+\dfrac{1}{2}=\dfrac{23}{23}+\dfrac{21}{21}+\dfrac{1}{2}=2+\dfrac{1}{2}=\dfrac{4+1}{2}=\dfrac{5}{2}\)
