Đáp án:
Bài `1`
`a,`
`7/(-25) + (-18)/25 + 4/23 + 5/7 + 19/23`
`= (7/(-25) + (-18)/25) + (4/23 + 19/23) + 5/7`
`= (-1) + 1 + 5/7`
`= 0 + 5/7`
`= 5/7`
`b,`
`7/19 × 8/11 + 7/19 × 3/11 + 12/19`
`= 7/19 × (8/11 + 3/11) + 12/19`
`= 7/19 × 1 + 12/19`
`= 7/19 + 12/19`
`=1`
`c,`
`8 2/7 - (3 4/9 + 4 2/7)`
`= 8 2/7 - 3 4/9 - 4 2/7`
`= (8 2/7 - 4 2/7) - 3 4/9`
`= 4 - 31/9`
`= 5/9`
`d,`
`(-7)/9 × 3/11 + (-7)/9 × 8/11 + 1 7/9`
`= (-7)/9 × (3/11 + 8/11) + 16/9`
`= (-7)/9 × 1 + 16/9`
`= (-7)/9 + 16/9`
`= 1`
`e,`
`7/35 × 10/19 + 7/35 × 9/19 - 2/35`
`= 7/35 × (10/19 + 9/19) - 2/35`
`= 7/35 × 1 - 2/35`
`= 7/35 - 2/35`
`= 1/7`
`f,`
`(-25) × 125 × 4 × (-8) × (-17)`
`= (-25 × 4) × (-8 × 125) × (-17)`
`= -100 × (-1000) × (-17)`
`= 100 000 × (-17)`
`= -17 00 000`
$\\$
Bài `2`
`a,`
`x - 2/3 = 3/5 - 1/4`
`-> x - 2/3 = 7/20`
`-> x = 7/20 + 2/3`
`-> x = 61/60`
Vậy `x = 61/60`
`b,`
`-2/3x + 1/5 = 1/10`
`-> -2/3x = 1/10 - 1/5`
`-> -2/3x = (-1)/10`
`-> x = (-1)/10 ÷ (-2)/3`
`-> x = 3/20`
Vậy `x = 3/20`
`c,`
`2 |1/2x - 1/3| - 3/2 = 1/4`
`-> 2 |1/2x - 1/3| = 1/4 + 3/2`
`-> 2 |1/2x - 1/3| = 7/4`
`-> |1/2x - 1/3| =7/4 ÷ 2`
`-> |1/2x - 1/3| = 7/8`
`->` \(\left[ \begin{array}{l}\dfrac{1}{2}x-\dfrac{1}{3}=\dfrac{7}{8}\\ \dfrac{1}{2}x-\dfrac{1}{3}=\dfrac{-7}{8}\end{array} \right.\)
`->` \(\left[ \begin{array}{l}\dfrac{1}{2}x=\dfrac{29}{24}\\ \dfrac{1}{2}x=\dfrac{-13}{24}\end{array} \right.\)
`->` \(\left[ \begin{array}{l}x=\dfrac{29}{12}\\x=\dfrac{-13}{12}\end{array} \right.\)
Vậy `x = 29/12` hoặc `x = (-13)/12`
`d,`
`4/5 - 1/2x = 1/10`
`-> 1/2x = 4/5 - 1/10`
`-> 1/2x = 7/10`
`-> x = 7/10 ÷ 1/2`
`-> x = 7/5`
Vậy `x= 7/5`
