Đáp án:
Bài `1`
`a,`
`(-7)/9 + 11/24 + (-5)/14 + 2/(-9) + 13/24`
`= ( (-7)/9 + 2/(-9) ) + (11/24 + 13/24) + (-5)/14`
`= -1 + 1 + (-5)/14`
`= 0 + (-5)/14`
`= (-5)/14`
`b,`
`16 3/31 - (19/28 + 10 3/31)`
`= 16 3/31 - 19/28 - 10 3/31`
`= (16 3/31 - 10 3/31) - 19/28`
`= 6 - 19/28`
`= 149/28`
`c,`
`15/49 - (80% + 2/3) ÷ 2 1/5`
`= 15/49 - 22/15 ÷ 11/5`
`= 15/49 - 2/3`
`= (-53)/147`
$\\$
Bài `2`
`a,`
`(2 4/5x - 50) ÷ 2/3 = 51`
`-> 14/5x - 50 = 51 × 2/3`
`-> 14/5x - 50 = 34`
`-> 14/5x = 34 + 50`
`-> 14/5x = 84`
`-> x= 84 ÷ 14/5`
`-> x = 30`
Vậy `x=30`
`b,`
`1/3 - x/2= 8/3 - 250%`
`-> 1/3 - x/2 = 1/6`
`-> x/2 =1/3 - 1/6`
`-> x/2 =1/6`
`-> 6x = 2`
`-> x = 2 ÷ 6`
`-> x = 1/3`
Vậy `x=1/3`
`c,`
`1/3 - |5/4 - 2x| = 1/4`
`-> |5/4 - 2x| = 1/3 - 1/4`
`-> |5/4 - 2x| = 1/12`
`->` \(\left[ \begin{array}{l}\dfrac{5}{4}-2x=\dfrac{1}{12}\\ \dfrac{5}{4}-2x=\dfrac{-1}{12}\end{array} \right.\)
`->` \(\left[ \begin{array}{l}2x=\dfrac{7}{6}\\2x=\dfrac{4}{3}\end{array} \right.\)
`->` \(\left[ \begin{array}{l}x=\dfrac{7}{12}\\x=\dfrac{2}{3}\end{array} \right.\)
Vậy `x=7/12` hoặc `x=2/3`
