Bài 1
a) 5/17 + -15/34 . 2/5
= 5/17 + 3/17
= 10/17
b) 1/2 . 5/6 + 2/3 . 3/4
= 5/12 + 6/12
= 11/12
c) (-2/5 + 1/3) . (3/2 - 3/7)
= -1/15 . 9/14
= -3/70
d) (1 + 1/2) . (1 + 1/3) . (1 + 1/4)
= 3/2 . 4/3 . 5/4
= 2/5
e) 1/5 : 1/10 - 1/3 (6/5 - 9/4) 
= 1/5 : 1/10 - 1/3 . -21/20
= 1/2 - (-7/20)
= 17/20
f ) -7/8 : 21/16 - 5/3 . (1/5 - 7/10)
= -7/8 : 21/16 - 5/3 . -1/2
= -2/3 - (-5/6)
= 1/6
g) 1/5 (1/2 - 1/3) : (-9/10) + -7/3
= 1/5 . 1/6 : (-9/10) + -7/3
= 1/30 : (-9/10) + -7/3
= 1/-27 + -7/3
= -50/27
Bài 2
a) 2/3 + (5/7 + -2/3)
= 2/3 + 5/7 + -2/3
= (2/3 + -2/3) + 5/7
= 5/7
b) 1/15 + 1/35 + 1/63 + 1/99 + 1/143
= 1/2 . (2/3.5 + 2/5.7 + 2/7.9 +2/9.11 + 2/11.13)
= 1/2 . (1/3 - 1/5 + 1/5 - 1/7 + 1/7 - 1/9 + 1/9 - 1/11 + 1/11 - 1/13)
= 1/2 . (1/3 - 1/13)
= 1/2 . 10/39
= 1/39
c) 1/5 . 4/7 + 3/7 . 1/5 - 1/5
= 1/5 . 4/7 + 3/7 . 1/5 - 1/5 . 1
= 1/5 . (4/7 + 3/7 + 1) 
=1/5 . 2
= 1/25
d) -1/9 . -3/5 + 5/-6 . -3/5 - 7/2 . 3/5
= -1/9 . -3/5 + 5/-6 . -3/5 + 7/2 . -3/5
= -3/5 . ( -1/9 + 5/-6 + 7/2)
= -3/5 . 16/9
= 16/15
e) 5/13 + -5/7 + -20/41 + 8/13 + -21/41
= (5/13 + 8/13) + (-20/41 + -21/41) + -5/7
= 1 + (-1) + -5/7
= -5/7
g) 6/7 . 8/13 + 6/7 . 9/13 - 3/13 . 6/7
= 6/7 . (8/13 + 9/13 - 3/13)
= 6/7 . 14/13
= 12/13
h) -3/7 . 15/13 - 3/7 . 11/13 - 3/7
= -3/7 . 15/13 - 3/7 . 11/13 - 3/7 . 1
= -3/7 . 15/13 + -3/7 . 11/13 + -3/7 . 1
= -3/7 . (15/13 + 11/13 + 1)
= -3/7 . 3
= -1/7
Bài 3
a) 60,7 + 25,5 - 38,7 
= (60,7 -38.7) + 25,5
= 22 + 25,5
= 47,5
b) (-9,207) + 3,8 + (-1,5030) - 2.8
= (-9,207) + 3,8 + (-1,503) - 2.8
= [-9,207 + (-1,503)] + (3,8 - 2,8)
= -10,71 + 1
= -9,71
c) (-12,5) + 17,55 + (-3,5) - (-2,45)
= (-12,5) + 17,55 + (-3,5) + 2,45
= [-12,5 + (-3,5)] + (17,55 + 2,45)
= -16 + 20
= 4
d) 2,07 + (-7,36) - (-8,97) + 1,03 -7,64
= 2,07 + (-7,36) + 8,97 + 1,03 + (-7,64)
= 2,07 + (8,97 + 1,03) + [-(7,36 + 7,64)] 
= 2,07 + 10 + (-15)
= 2,93
e) -23.25 + (-25,18)
= -48,43
f ) 27,35 + (-17,25)
=10,1
g) (-0,4) . (-0,5) . (-0,8)
= 0,2 . (-0,8)
= -0,16
h) (-1,6) . (-0,125) . (-0,5)
= 0,2 . (-0,5)
= -0,1
i ) 3,58 . 34,45 + 3,58 . 75,55
= 3,58 . (34,45 + 75,55)
= 3,58 . 110
= 393,8
k) 3,4 . (-23,68) - 3,4 . 45,12 + (-31,2) . 3,4
= 3,4 . (-23,68) + 3,4 . (-45,12) + (-31,2) . 3,4
= 3,4 . [-(23,68 + 45,12 + 31,2)]
= 3,4 . 100
= 340
Bài 3: Tìm x
a) x = -1/4 + 2/13
    x = 21/52
b) x/3 = 2/3 + -1/7
    x/3 = 11/21
<=> x . 21 = 3 . 11
<=> x . 21 = 33
<=> x        = 33 : 21
<=> x        = 33/21
c) -5/6 - x = 7/12 + -1/3
    -5/6 - x = 1/4
             x = -5/6 - 1/4
             x = -13/12
d) 5 (x - 3) = 5/7
        x - 3   = 5/7 : 5
        x - 3   = 1/7
        x        = 1/7 + 3
        x        = 22/7
e) -4 (x - 1/3 ) = -8/3
         x - 1/3    = -8/3 : (-4)
         x - 1/3    = 2/3
         x            = 2/3 + 1/3
         x            = 1
f ) x + 2/3 = -1/12 . -4/5
    x + 2/3 = 1/15
    x          = 1/15 - 2/3 
    x          = -3/15
Bài 4
a) x - 3/10 = 7/15 : 3/5
    x - 3/10 = 7/9
    x           = 7/9 + 3/10
    x           = 97/90
b) x + 3/22 = 27/121 . 11/9
    x + 3/22 = 3/11
    x            = 3/11 - 3/22
    x            = 3/22
c) 8/23 . 46/24 = 1/3 . x
                  2/3 =1/3 . x
                     x = 2/3 : 1/3
                     x = 2
d) 1/5 : x = 1/5 - 1/7
    1/5 : x = 2/35
            x = 1/5 : 2/35
            x = 7/2