câu a : 

\(\dfrac{-8}{24}+\dfrac{-4}{12}=\dfrac{-1}{3}+\dfrac{-1}{3}=\dfrac{-2}{3}\)

câu b : 

\(\dfrac{-20}{35}+\dfrac{16}{24}=\dfrac{-4}{7}+\dfrac{2}{3}=\dfrac{2}{21}\)

câu c : 

\(\dfrac{-3}{9}+\dfrac{-6}{15}=\dfrac{-1}{3}+\dfrac{-2}{5}=\dfrac{-11}{15}\)

câu d : 

\(\dfrac{3}{13}-\dfrac{4}{10}=\dfrac{3}{13}-\dfrac{2}{5}=\dfrac{-11}{65}\)

câu e : 

\(\dfrac{5}{17}-\dfrac{9}{15}=\dfrac{5}{17}-\dfrac{3}{5}=\dfrac{-26}{85}\)

câu g : 

\(\dfrac{9}{18}-\dfrac{6}{15}+\dfrac{3}{-9}=\dfrac{9}{18}-\dfrac{6}{15}+\dfrac{-3}{9}\\ =\dfrac{1}{2}-\dfrac{2}{5}+\dfrac{-1}{3}=\dfrac{-7}{30}\)

câu h : 

\(\dfrac{5}{4}-\dfrac{1}{2}+\dfrac{-7}{8}=\dfrac{10}{8}-\dfrac{4}{8}+\dfrac{-7}{8}=\dfrac{-1}{8}\)

\(b=\text{​​}\dfrac{15.2^{24}.3^{14}-4.3^{15}.2^{24}}{19.2^{24}.3^{14}-6.2^{24}.3^{15}}=\)

\(=\dfrac{2^{24}.3^{14}\left(15-4.3\right)}{2^{24}.3^{14}\left(19-6.3\right)}=3\)

27/15 + 6/8 =51/20
19/24 + 7/18 = 85/72
2/9 - 1/6 = 1/18
8/15 -1/3 = 1/5

câu đầu có \(3-12\sqrt{6}< 0\) nên không căn được nên đề bạn sai

\(\sqrt{31-8\sqrt{15}}+\sqrt{24-6\sqrt{15}}\)

\(=\sqrt{4^2-2.4.\sqrt{15}+\left(\sqrt{15}\right)^2}+\sqrt{\left(\sqrt{15}\right)^2-2.\sqrt{15}.3+3^2}\)

\(=\sqrt{\left(4-\sqrt{15}\right)^2}+\sqrt{\left(\sqrt{15}-3\right)^2}=\left|4-\sqrt{15}\right|+\left|\sqrt{15}-3\right|\)

\(=4-\sqrt{15}+\sqrt{15}-3=1\)

\(\sqrt{49-5\sqrt{96}}-\sqrt{49+5\sqrt{96}}=\sqrt{49-20\sqrt{6}}-\sqrt{49+20\sqrt{6}}\)

\(=\sqrt{5^2-2.5.2\sqrt{6}+\left(2\sqrt{6}\right)^2}-\sqrt{5^2+2.5.4\sqrt{6}+\left(2\sqrt{6}\right)^2}\)

\(=\sqrt{\left(5-2\sqrt{6}\right)^2}-\sqrt{\left(5+2\sqrt{6}\right)^2}=\left|5-2\sqrt{6}\right|-\left|5+2\sqrt{6}\right|\)

\(=5-2\sqrt{6}-5-2\sqrt{6}=-4\sqrt{6}\)

\(\sqrt{31-8\sqrt{15}}+\sqrt{24-6\sqrt{15}}\)

\(=4-\sqrt{15}+\sqrt{15}-3\)

=1

a)9/8

b)1/12

a)7/8 + 1 - 3/4

= 7/8 + 8/8- 6/8

=9/8

b) 15/24 - 3/8 - 1/6

=15/8 - 9/24 - 4/24

=2/24=1/12

a)7/8 + 1 - 3/4

= 7/8 + 8/8- 6/8

=9/8

b) 15/24 - 3/8 - 1/6

=15/8 - 9/24 - 4/24

=2/24=1/12

`@` `\text {Ans}`

`\downarrow`

`1,`

`a)`

`-7/25 + (-8)/25`

`= (-7 - 8)/25`

`= -15/25`

`= -3/5`

`b)`

`6/13 + (-15)/39`

`= 18/39 + (-15)/39`

`= (18 - 15)/39`

`= 3/39`

`= 1/13`

`c)`

`5/7 + 4/(-14)`

`= 10/14 + (-4)/14`

`= (10 - 4)/14`

`= 6/14`

`= 3/7`

`d)`

`-8/18 + (-15)/27`

`= -4/9 + (-5)/9`

`= (-4-5)/9`

`= -9/9 = -1`

`2,`

`a)`

`3/5 + (-7)/4`

`= 12/20 + (-35)/20`

`= (12 - 35)/20`

`=-23/20`

`b)`

`(-2) + (-5)/8`

`= (-16)/8 + (-5)/8`

`= (-16 - 5)/8`

`= -21/8`

`c)`

`1/8 + (-5)/9`

`= 9/72 + (-40)/72`

`= (9-40)/72`

`= -31/72`

`d)`

`6/13 + (-14)/39`

`= 18/39 + (-14)/39`

`= (18 - 14)/39`

`= 4/39`

`e)`

`(-18)/24 + 15/21`

`= (-3)/4 + 5/7`

`= (-21)/28 + 20/28`

`= (-21 + 20)/28`

`= -1/28`

Ta có:

67 - [ 8 + 7 . 3² - 24 : 6 + ( 9 - 7 )³ ] : 15 

= 67 - (8 + 7.9 - 4 + 8) : 15

= 67 - 75 : 15

= 67 - 5

= 62