Đáp án:
Bài 1
`a, 11 3/13 - (2 + 3/13)`
`= 11 3/13 - 2 - 3/13`
`= (11 3/13 - 3/13) - 2`
`= 11 - 2`
`= 9`
`b, (-5)/7 . 2/11 + (-5)/7 . 9/11 + 5/7`
`= 5/7 . (-2/11 + (-9)/11 + 1)`
`= 5/7 . 0`
`= 0`
`c, 4 7/10 + (2/5 - 1/10)`
`= 47/10 + 3/10`
`= 5`
`d, 3/(10 . 12) + 3/(12 . 14) + 3/(14 . 16) + ... + 3/(48 . 50)`
`= 3 . (1/(10 . 12) + 1/(12 . 14) + 1/(14 . 16) + ... + 1/(48 . 50) )`
`= 3 . 1/2 . (1/10 - 1/12 + 1/12 - 1/14 + 1/14 - 1/16 + ... + 1/48 - 1/50)`
`= 3/2 . (1/10 - 1/50)`
`= 3/2 . 2/25`
`= 3/25`
Bài 2
`a, 4/5x = 4/7`
`-> x = 4/7 : 4/5`
`-> x = 5/7`
Vậy `x = 5/7`
`b, 3/4 + 1/4 : x = 1`
`-> 1/4 : x = 1 - 3/4`
`-> 1/4 : x = 1/4`
`-> x = 1/4 : 1/4`
`-> x = 1`
Vậy `x = 1`
`c, x : 8/11 = 11/3`
`-> x = 11/3 . 8/11`
`-> x = 8/3`
Vậy `x = 8/3`
`d, |x - 1| - 2 =0`
`-> |x - 1| = 2`
`->` \(\left[ \begin{array}{l}x-1=2\\x-1=-2\end{array} \right.\)
`->` \(\left[ \begin{array}{l}x=3\\x=-1\end{array} \right.\)
Vậy `x = 3` hoặc `x = -1`
