`a) 15 3/13 - (3 4/7 + 8 3/13)`
`= 15 3/13 - 3 4/7 - 8 3/13`
`= (15 3/13 - 8 3/13) - 3 4/7`
`= 7 - 3 4/7`
`= 4 4/7`
`= 37/7`
`b) (7 4/9 + 4 7/11) - 3 4/9`
`= (7 4/9 - 3 4/9) + 4 7/11`
`= 4 + 4 7/11`
`= 8 7/11`
`= 95/11`
`c) -7/9. 4/11 + -7/9. 7/11 + 5 7/9`
`= -7/9. (4/11 + 7/11) + 5 7/9`
`= -7/9. 1 + 5 7/9`
`= -7/9 + 5 7/9`
`= 5`
`d) 50%. 1 1/3 . 10. 7/35 . 0,75`
`= 1/2. 4/3. 10. 1/5. 3/4`
`= (1/2. 1/5. 10). (4/3. 3/4)`
`= (1/10 . 10). 1`
`= 1. 1`
`= 1`
`e) 3/(1.4) + 3/(4.7) + 3/(7.10) + ... + 3/(40.43)`
`= 1 - 1/4 + 1/4 - 1/7 + 1/7 - 1/10 + ... + 1/40 - 1/43`
`= 1 - 1/43`
`= 42/43`
`**)` Kiến thức cần nhớ!
`(|a-b|)/(a.b) = 1/a - 1/b (a, b \ne 0)`
