Bài `1:`
`a) (-4)/9 . 7/15 + 4/(-9) . 8/15`
` = (-4)/9 . 7/15 + (-4)/9 . 8/15`
`= (-4)/9. (7/15 + 8/15)`
` = (-4)/9 . 1`
` = (-4)/9`
`e) 11 1/4 - (2 5/7 + 5 1/4)`
` = 11 + 1/4 - (2+5/7+ 5 + 1/4)`
` = 11+1/4 - 2-5/7-5-1/4`
` = (11-2-5) - 5/7 + (1/4-1/4)`
` = 4 - 5/7 `
` = 28/7 - 5/7`
` = 23/7`
`c) 4 11/23 - 9/14 + 2 12/23 - 5/4`
` = 4 + 11/23 - 9/14 + 2 + 12/23 - 5/4`
` = (4+2) + (11/23 + 12/23) - (9/14 + 5/4)`
` = 6 + 1 - 53/28`
` = 7 - 53/28`
` = 143/28`
Bài `2:`
`a) 3/4 . 16/9 - 7/5 : (-21)/20`
` = 3/4 . 16/9 - 7/5 . (-20)/21`
` = 4/3 - (-4/3)`
` = 4/3 + 4/3`
` = 8/3`
`c) (20+ 9 1/4) : 2 1/4`
` = 117/4 : 9/4`
` = 117/4 . 4/9`
` = 117/9 =13`
`e) 32/15 : (-1 1/5 + 1 1/3)`
`= 32/15 : [(-1+1) + ((-1)/5 + 1/3)]`
` = 32/15 : ((-1)/5+1/3)`
` = 32/15 : 2/15`
` = 32/15 . 15/2`
` = 32/2 = 16`
`h) 1 13/15 . 0,75 - (8/15 + 0,25) .24/47`
` = 28/15 . 3/4 - (8/15 + 1/4) . 24/47`
` = 7/5 - 47/60 . 24/47`
` = 7/5 - 2/5`
` =5/5 = 1`
Bài `3:`
`a) x : 3 1/15 = 1 1/2`
` => x : 46/25 = 3/2`
` => x = 3/2 . 46/25`
` => x = 23/5`
Vậy `x=23/5`
`c) 7x-3x=3,2`
`=> 4x = 3,2`
`=> x = 3,2 :4`
`=> x= 0,8`
Vậy `x=0,8`
`e) 2 1/4 . (x- 7 1/3) =1,5`
`=> x - 7 1/3 = 1,5 : 2 1/4`
`=> x - 22/3 = 2/3`
`=> x = 2/3 + 22/3`
`=> x = 24/3 =8`
Vậy `x=8`